Update golang version to latest + streamline build

[0xdevalias]

Gobuster seems to be built against golang 1.6, which is pretty dated now.

It would be good to update this, and possibly even make use of the official go containers for building, and maybe multi build stages to cut down on container size.

For example, this is the Dockerfile I put together to build a tiny gobuster image (~1mb total), could follow a similar pattern maybe?

• https://github.com/0xdevalias/docker-gobuster/blob/master/Dockerfile
• https://hub.docker.com/r/devalias/gobuster/tags/

I also noticed that altdns seems to include go, yet doesn't appear to use it as it's python based?

• https://github.com/anshumanbh/brutesubs/blob/master/tools/altdns/Dockerfile#L28-L34

Could probably be removed?

[anshumanbh]

@0xdevalias I don't maintain brutesubs anymore. I've built a better version of this already.

[0xdevalias]

That's fair enough. Maybe drop a note in the README or something saying unmaintained so it's more obvious? And if the replacement is public, possibly linking to that as the new version.