cmd/gopherbot: add the author of the change to the notification on github

[codebien]

When a new change is pushed, the gopherbot posts a new message on Github following this new format:
Change https://golang.org/cl/NNNN by AUTHOR mentions this issue

A new method to the CL's API in the maintner package is added
to provide the related absolute url.

Fixes golang/go#26816

[gopherbot]

This PR (HEAD: 590a834) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/build/+/181977 to see it.

Tip: You can toggle comments from me using the comments slash command (e.g. /comments off)
See the Wiki page for more info

[gopherbot]

Message from Gobot Gobot:

Patch Set 1:

Congratulations on opening your first change. Thank you for your contribution!

Next steps:
Within the next week or so, a maintainer will review your change and provide
feedback. See https://golang.org/doc/contribute.html#review for more info and
tips to get your patch through code review.

Most changes in the Go project go through a few rounds of revision. This can be
surprising to people new to the project. The careful, iterative review process
is our way of helping mentor contributors and ensuring that their contributions
have a lasting impact.

During May-July and Nov-Jan the Go project is in a code freeze, during which
little code gets reviewed or merged. If a reviewer responds with a comment like
R=go1.11, it means that this CL will be reviewed as part of the next development
cycle. See https://golang.org/s/release for more details.

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/181977.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Andrew Bonventre:

Patch Set 2:

(1 comment)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/181977.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

This PR (HEAD: ebf4772) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/build/+/181977 to see it.

Tip: You can toggle comments from me using the comments slash command (e.g. /comments off)
See the Wiki page for more info

[gopherbot]

Message from Ivan Palladino:

Patch Set 4: Commit message was updated.

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/181977.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Ivan Palladino:

Patch Set 5:

(2 comments)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/181977.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Andrew Bonventre:

Patch Set 5:

(1 comment)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/181977.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Go Bot:

Patch Set 1:

Congratulations on opening your first change. Thank you for your contribution!

Next steps:
Within the next week or so, a maintainer will review your change and provide
feedback. See https://golang.org/doc/contribute.html#review for more info and
tips to get your patch through code review.

Most changes in the Go project go through a few rounds of revision. This can be
surprising to people new to the project. The careful, iterative review process
is our way of helping mentor contributors and ensuring that their contributions
have a lasting impact.

During May-July and Nov-Jan the Go project is in a code freeze, during which
little code gets reviewed or merged. If a reviewer responds with a comment like
R=go1.11, it means that this CL will be reviewed as part of the next development
cycle. See https://golang.org/s/release for more details.

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/181977.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Gopher Robot:

Patch Set 1:

Congratulations on opening your first change. Thank you for your contribution!

Next steps:
Within the next week or so, a maintainer will review your change and provide
feedback. See https://golang.org/doc/contribute.html#review for more info and
tips to get your patch through code review.

Most changes in the Go project go through a few rounds of revision. This can be
surprising to people new to the project. The careful, iterative review process
is our way of helping mentor contributors and ensuring that their contributions
have a lasting impact.

During May-July and Nov-Jan the Go project is in a code freeze, during which
little code gets reviewed or merged. If a reviewer responds with a comment like
R=go1.11, it means that this CL will be reviewed as part of the next development
cycle. See https://golang.org/s/release for more details.

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/181977.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Andrew Bonventre:

Patch Set 2:

(1 comment)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/181977.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Ivan Palladino:

Patch Set 4: Commit message was updated.

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/181977.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Ivan Palladino:

Patch Set 5:

(2 comments)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/181977.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Andrew Bonventre:

Patch Set 5:

(1 comment)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/181977.
After addressing review feedback, remember to publish your drafts!