Replace Travis CI with GitHub Actions

[maartenpaauw]

Title says all

[neelkamath]

I'll do it

[neelkamath]

This issue is labeled as "hacktoberfest", but is ineligible for it:

This is either because you need to re-add the hacktoberfest label (perhaps because you added it before October), or you need to add the hacktoberfest topic to your repo's topics temporarily.

[maartenpaauw]

I've merged the PR but it is not working perfectly. The linter is now linting the workflow file and not the theme.

[neelkamath]

@maartenpaauw change line 10 of the workflow to yamllint themes/template.yaml then. I wasn't sure whether you wanted to lint all YAML files or not.

[maartenpaauw]

There is a .yamllint config file with configuration that points to the template.yaml file. It worked before with Travis CI. Not sure why its not working with GitHub actions.

[neelkamath]

Ohh.
By the way, I seem to have forgotten to replace the Travis CI badge in the README with the GitHub Actions one.