Invalid HTTP method will raise I18n::InvalidLocale if :en is not a valid locale.

`Request#check_method` uses `to_sentence(locale: :en)`, which raises `I18n::InvalidLocale` when `I18n.available_locales` does not include `:en` and `I18n.enforce_available_locales` is `true` (default).

I inlined the `to_sentence` functionality in `check_method` to solve this. Not sure if this is the best solution, but it works.

**NOTE:** `ActionController::MethodNotAllowed` has a similar problem, but I don't know where that is tested or if it's even used anywhere.