feat: Add spell-checking for GitLab

[hyperupcall]

This adds spell checking for GitLab. I've seen this in the wild in repositories like awesome-zsh-plugins.

Output of yarn test test/rules/spell-check.js

$ yarn test test/rules/spell-check.js

yarn run v1.22.19
xo && ava test/rules/spell-check.js

  rules/spell-check.js:42:7
  ⚠   42:7   Blocks are nested too deeply (5). Maximum allowed is 4.               max-depth
  ⚠   46:7   Blocks are nested too deeply (5). Maximum allowed is 4.               max-depth

  test/api.js:10:1
  ⚠   10:1   Unexpected todo comment: TODO: Uncomment this when the issue is....   no-warning-comments

  rules/contributing.js:11:2
  ⚠   11:2   Unexpected todo comment: TODO: This doesn't work on Linux for....     no-warning-comments

  index.js:105:25
  ⚠  105:25  Unexpected todo comment: TODO: because of....                         no-warning-comments

  config.js:21:2
  ⚠   21:2   Unexpected todo comment: TODO: this rule doesn't properly handle....  no-warning-comments

  6 warnings


  2 tests passed

Done in 2.54s.