Run linters from workspace root

[FooBarWidget]

Fixes #717.

• The build passes
• TSLint is mostly happy — It was already unhappy. This PR doesn't make it more unhappy.
• Prettier has been run — Not possible because TSLint was already unhappy through no fault of this PR.

[codecov]

Codecov Report

Merging #718 (46ee01c) into master (7b5b602) will not change coverage.
The diff coverage is 0.00%.

@@          Coverage Diff           @@
##           master    #718   +/-   ##
======================================
  Coverage    5.08%   5.08%           
======================================
  Files          10      10           
  Lines         118     118           
  Branches       20      20           
======================================
  Hits            6       6           
  Misses        112     112           

Flag	Coverage Δ
language_server_ruby	5.08% <0.00%> (ø)

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Impacted Files	Coverage Δ
packages/language-server-ruby/src/Linter.ts	0.00% <0.00%> (ø)

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[github-actions]

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[FooBarWidget]

Closing this PR because of #717 (comment)

Running linters not from the workspace root is in fact intentional.