make error page display work in Rails 5
make error page display work in Rails 5

In Rails 5, if app inherited `ActionController::Metal`, is treated as a
controller, `.call` are no longer called.
Therefore, it is made to the handling of the action name in `#process` instead.

Ref: https://github.com/rails/rails/commit/a26033b

yuki24/rambulance,yuki24/rambulance