[Rails5] Add `raise: false` to skip_before_action in authenticates_with_two_factor.rb

Rails 5.0 raises `ArgumentErrror` if an unrecognised callback is skipped.
https://github.com/rails/rails/commit/8b88df94ebda2e829782f514ff51caeaf5e694dd
This commit adds `raise: false` to the filter.