If for some reason `Discourse.store.path_for` returns `nil`, the
forum would throw an error rather than returning 404.
Why would it be `nil`? One cause could be changing the type of
file store and having the `url` field no longer be relative.
This updates tests to use latest rails 5 practice
and updates ALL dependencies that could be updated
Performance testing shows that performance has not regressed
if anything it is marginally faster now.
Guo Xiang Tan
Robin Ward
Bianca Nenciu
Sam
Guo Xiang Tan
OsamaSayegh