Fix #3372, run server unit tests with npm run test

[ianb]

Note tests have broken when they weren't being run.

I'm not that clear on how the tests should act, so I'm not sure how to fix. Errors:

  1) l10n middleware getLanguage function (Accept-Language header parsing) should return ["en-US"] if Accept-Language header value is "en-CA":

      AssertionError: 'en-US' == 'en-CA'
      + expected - actual

      -en-US
      +en-CA
      
      at Context.it (test/server/unit/middleware/l10n-test.js:24:14)

  2) l10n middleware getLanguage function (Accept-Language header parsing) should return ["en-US"] if Accept-Language header value is "en":

      AssertionError: 'en-US' == 'en'
      + expected - actual

      -en-US
      +en
      
      at Context.it (test/server/unit/middleware/l10n-test.js:30:14)