Add required parameter to code search spec.

The search code api requires a user, organization or repository to
search for code, unfortunately. `user:github` added to test query.
Assert existence instead of exact value in Meta Spec.
Fix Gist spec for vnd.github.v3 media type response.

Changed gist.user to gist.owner references for vnd.github.v3 media type.
Add call to star_gist in before method for .gist_starred? test.
Merge pull request #421 from joeyw/fix-gist-spec

Fix Gist spec for vnd.github.v3 media type response.
Merge pull request #420 from joeyw/fix-meta-spec

Assert existence instead of exact value in Meta Spec.
Merge pull request #419 from joeyw/fix-code-search-spec

Add required parameter to code search spec.