Remove header property value validation

[refactornator]

This PR removes property validation for header properties.

What kind of change does this PR introduce?

bugfix

Did you add or update the examples/?
No changes were necessary.

Summary

The validation that was being used before this PR was preventing multiple cookies from being set (Set-Cookie), or multiple domains being used (Access-Control-Allow-Origin). The 'http' server supports strings or arrays, so this validation was preventing this functionality from working.

#964

Does this PR introduce a breaking change?

No

Other information

[jsf-clabot]

All committers have signed the CLA.

[shellscape]

As a slight modification to your original PR description, this PR doesn't remove validation of header properties, but rather header property values.

Citing the spec is also useful when submitting PRs for scheme validation changes: https://trac.tools.ietf.org/html/draft-wright-json-schema-validation-01#page-11

The documentation will have to be changed once this is merged and published: https://webpack.js.org/configuration/dev-server/#devserver-headers-

[shellscape]

Before we can approve this change, we need to add an additional test for headers set to an array, after this test:

webpack-dev-server/test/Routes.test.js

Line 60 in 69239ce

it('GET request with headers', (done) => {

[refactornator]

@shellscape Thanks for your quick response on this, looking forward to getting this included so we can use webpack-dev-server again.

[codecov]

Codecov Report

Merging #1115 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #1115   +/-   ##
======================================
  Coverage    76.8%   76.8%           
======================================
  Files           5       5           
  Lines         470     470           
  Branches      151     151           
======================================
  Hits          361     361           
  Misses        109     109

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[shellscape]

@wlindner ping. please see comments.

[refactornator]

@shellscape I just pushed a new commit that includes tests. I went ahead and restructured the tests in this file so that I could properly do the test setup: one testing headers as a string and one as an array. If this is not how you want it to be structured please let me know.

[shellscape]

@wlindner thanks for making those updates, and all your work on this PR so far. you've still got a linting error in CI that needs addressing, and the branch is out of date and should be updated.

[refactornator]

@shellscape I've made all the changes you requested, and tests and linting passed locally. But, it looks like it's failing for node 6 with a route test in CI. I moved the describe blocks around in that test file, but didn't change any of the content of those tests and I don't think it's related to the header validation change. Any suggestions for what I should do to fix this so CI passes?

[shellscape]

@wlindner looks like you still have an issue with CI. Click the "details" link for the "continuous-integration/travis-ci/pr" item and examine the log to find out what's causing an issue. We can't merge until that's resolved.

[refactornator]

@shellscape ok, I think I did all the things you needed to prepare this PR. Let me know if I missed anything.