resolves #245 adding support for pikchr

[juracy]

No description provided.

[ggrossetie]

Thanks @juracy for your contribution 🎉
I'm glad that you took care of this issue. Since this is your first contribution on this repository, feel free to share things that we can improve to make it easier to contribute.

Tests are failing but this is not related to your changes. I've deployed a new version of https://kroki.io (0.13.0) and I need to update the fixtures/assertions.

[ggrossetie]

@juracy I fixed master and rebase your branch

[juracy]

Thanks @Mogztter, maybe a Contribution Guide may help new contributors...

And my original PR passed through lint check, but it isn't passing now with your changes ...

> standard src/**.js test/**.js

standard: Use JavaScript Standard Style (https://standardjs.com)
standard: Run `standard --fix` to automatically fix some problems.
  /home/juracy/workspace/asciidoctor-kroki/test/test.spec.js:966:1: Expected indentation of 6 spaces but found 0.

[ggrossetie]

Thanks @Mogztter, maybe a Contribution Guide may help new contributors...

OK 👍🏻

And my original PR passed through lint check, but it isn't passing now with your changes ...

Ooops my bad, I will fix it.

[ggrossetie]

And merged! Thanks again 👏🏻