Fix mentionable spec

spec/support/mentionable_shared_examples.rb

@@ -11,7 +11,7 @@ def common_mentionable_setup
 
   let(:mentioned_issue) { create :issue, project: mproject }
   let(:other_issue) { create :issue, project: mproject }
-  let(:mentioned_mr) { create :merge_request, source_project: mproject, source_branch: 'different' }
+  let(:mentioned_mr) { create :merge_request, :simple, source_project: mproject }
   let(:mentioned_commit) { double('commit', sha: '1234567890abcdef').as_null_object }
 
   # Override to add known commits to the repository stub.
@@ -29,11 +29,7 @@ def common_mentionable_setup
     # unrecognized commits.
     commitmap = { '123456' => mentioned_commit }
     extra_commits.each { |c| commitmap[c.sha[0..5]] = c }
-
-    repo = double('repository')
-    repo.stub(:commit) { |sha| commitmap[sha] }
-    mproject.stub(repository: repo)
-
+    mproject.repository.stub(:commit) { |sha| commitmap[sha] }
     set_mentionable_text.call(ref_string)
   end
 end