Add syntax highlighting for svelte

[umanghome]

Resolves #4321 by adding syntax highlighting to .svelte files. Reopening after changes made to #4323.

Description

Checklist:

• I am associating a language with a new file extension.

  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • https://github.com/search?utf8=%E2%9C%93&type=Code&ref=searchresults&q=extension%3AFOOBAR+KEYWORDS+NOT+nothack
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• I am adding a new language.

  • The extension of the new language is used in hundreds of repositories on GitHub.com.
    • Search results for each extension:
      • https://github.com/search?q=extension%3Asvelte+NOT+nothack&type=Code
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample license(s):
      • TodoMVC.svelte: Unlicensed
  • I have included a syntax highlighting grammar: https://github-lightshow.herokuapp.com/
  • I have updated the heuristics to distinguish my language from others using the same extension.

• I am fixing a misclassified language

  • I have included a new sample for the misclassified language:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• I am changing the source of a syntax highlighting grammar

  • Old: https://github-lightshow.herokuapp.com/
  • New: https://github-lightshow.herokuapp.com/

• I am updating a grammar submodule

• I am adding new or changing current functionality

  • I have added or updated the tests for the new or changed functionality.

• I am changing the color associated with a language

  • I have obtained agreement from the wider language community on this color change.
    • [URL to public discussion]
    • [Optional: URL to official branding guidelines for the language]

[lildude]

As just discovered and mentioned in #4481, Travis CI doesn't support draft PRs yet, so once this is ready to go, you'll either need to push another commit after making this a real PR or we'll need to close and re-open it to trigger the build.

[umanghome]

This PR should be squash-merged.

[pchaigno]

Thanks for the pull request!

Could you please fill in the template? It is missing a correct link to in-the-wild search results and information on the added sample file. The Travis-CI build failure is also legit and should be addressed.

[umanghome]

@pchaigno I've updated the PR, let me know if it's still missing anything.

[lildude]

Thanks for updating the template, however it's missing one thing: the source of the sample file, which is also the reason I'm requesting a change on this PR. Your sample file looks like a very simple "hello world" example. No one uses "hello world" in production 😉 and they're not good for Linguist as they're terrible examples for training the classifier.

Can you please replace this with an appropriately licensed real-world example that makes a good representation of real usage, and link to the source in the template.

[umanghome]

@lildude I've added another example. Let me know if it's still trivial, I'll ask someone from the community to add one.

[lildude]

@umanghome looks good to me. Thanks.

[Alhadis]

LGTM. 👍

Changes have been implemented.

[pchaigno]

Syntax highlighting looks good too.