Lint: Enforce quotes

[fregante]

If there's a lint, follow it and enforce it, otherwise it just adds noise.

Before

❯ grunt eslint
Running "eslint:src" (eslint) task


Running "eslint:test" (eslint) task

./test/fixtures/detect-existing-browser-api-object/content.js
  40:42  warning  Strings must use doublequote  quotes
  41:14  warning  Strings must use doublequote  quotes
  43:30  warning  Strings must use doublequote  quotes
  48:36  warning  Strings must use doublequote  quotes
  50:36  warning  Strings must use doublequote  quotes
  51:47  warning  Strings must use doublequote  quotes

✖ 6 problems (0 errors, 6 warnings)
  0 errors and 6 warnings potentially fixable with the `--fix` option.


Done.

After

grunt eslint
Running "eslint:src" (eslint) task


Running "eslint:test" (eslint) task


Done.

[codecov]

Codecov Report

Merging #355 (9dcbf2f) into master (2d75968) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #355   +/-   ##
=======================================
  Coverage   91.03%   91.03%           
=======================================
  Files           1        1           
  Lines         145      145           
=======================================
  Hits          132      132           
  Misses         13       13           

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[Rob--W]

Thanks.

[fregante]

Should this be merged before any conflicts arise?