upgrade(rails 5): no longer use rake to invoke rake tasks, use rails

though I left the case alone where the command would previously been
just `bundle exec rake`, as doing the same doesn't work for rails.

config/database.yml

@@ -19,7 +19,7 @@ mysql:
   password:
 
 # Warning: The database defined as "test" will be erased and
-# re-generated from your development database when you run "rake".
+# re-generated from your development database when you run "rails".
 # Do not set this db to the same as development or production.
 test:
   adapter: sqlite3