Make mungegithub follow github changes

This makes mungegithub follow github changes to avoid errors::

 mungegithub/github/github.go:723:29: cannot use
   prot.RequiredPullRequestReviews (type *github.PullRequestReviewsEnforcement)
   as type *github.PullRequestReviewsEnforcementRequest in field value
 mungegithub/github/github.go:1360:10: cannot use
   listOpts (type *github.ListOptions)
   as type *github.ListCollaboratorsOptions in argument to
   config.client.Repositories.ListCollaborators

mungegithub/github/github.go

@@ -1353,7 +1353,7 @@ func (config *Config) fetchAllCollaborators() ([]*github.User, error) {
 	var result []*github.User
 	for {
 		glog.V(4).Infof("Fetching page %d of all users", page)
-		listOpts := &github.ListOptions{PerPage: 100, Page: page}
+		listOpts := &github.ListCollaboratorsOptions{PerPage: 100, Page: page}
 		users, response, err := config.client.Repositories.ListCollaborators(
 			context.Background(),
 			config.Org,