Add support for Vala-Lint

[atsuya]

Hi,

I added support for Vala-Lint. I've been using it myself, and it's working just fine.

Let me know if you have any questions. Thanks!

[atsuya]

@hsanson Thanks for your review. I applied suggested changes. Please take a look and let me know what you think. Thanks!

[hsanson]

This is good to merge. Waiting for Travis-CI to get fixed so all checks pass before merging.

[atsuya]

Great! I'm holding my 🍺️ until Travis-CI gets fixed.

[hsanson]

ALE migrated from Travis to Github Actions (see #3548) so it is necessary to rebase this PR from latest master branch to trigger the required checks.

# Add dense-analysis as remote upstream on your local fork. Not 
# needed if already added.
git remote add upstream https://github.com/dense-analysis/ale.git

# Sync your local master with upstream master
git checkout master
git fetch upstream master
git merge upstream/master

# Rebase the PR branch with master
git checkout my-branch-name
git rebase master   # Fix any conflicts you may have

# Force push the updated PR branch to origin to trigger the checks
git push -f origin my-branch-name

[atsuya]

Done. I also updated the linter name to snake case as the test indicated.

[hsanson]

Good to go, thanks.

[atsuya]

Cheers! 🍻