Button up adding support for require_code_owners_review

[thomasbrezinski]

This pull request includes @denniswebb's changes from https://github.com/terraform-providers/terraform-provider-github/pull/51 with the addition of the error check that was requested in the original PR.

From the original PR:
`
This PR adds support for require_code_owner_reviews for pull request review branch protection.

Updating the github.com/google/go-github vendored library was required for this support.

Other changes:

• Fix failing test TestAccGithubBranchProtection_basic by adding step to delete PullRequestReview settings if nil because github API does not remove when set to nil in branch protection requests.
• Updated resource_github_repository_collaborator to use ListCollaboratorsOptions due to change in go-github library
• Fixed failing tests TestAccGithubRepositoryDeployKey_basic
  `

Could we possibly merge the original PR then this one or just this one if nobody would mind? I'm in the process of trying to open source a terraform module that relies on this functionality.

[thomasbrezinski]

@radeksimko thoughts?

[thomasbrezinski]

Closing since https://github.com/terraform-providers/terraform-provider-github/pull/51 has been updated