In the Snippets::NotesController the noteable was resolved and
authorized through the :snippet_id, so by passing a :target_id for a
different snippet it was possible to create a note on a snippet
where the user would be unauthorized to do so otherwise.
This fixes the problem by ignoring the :target_id and :target_type from
the request, and using the same noteable for creation and authorization.
Updates specs to use new rails5 format.
The old format:
`get :show, { some: params }, { some: headers }`
The new format:
`get :show, params: { some: params }, headers: { some: headers }`
