[ci-skip] spec for an instance method

spec/lib/gitlab/git/diff_spec.rb

@@ -273,7 +273,7 @@ EOT
     end
   end
-  describe '.json_safe_diff' do
+  describe '#json_safe_diff' do
     let(:project) { create(:project, :repository) }
     it 'fake binary message when it detects binary' do