Change flash message to alert instead of error

Devise uses the defaults :notice and :alert everywhere, this one seems to
have been missed since it was introduced in
ff75341c75.

app/controllers/devise/passwords_controller.rb

@@ -53,7 +53,7 @@ class Devise::PasswordsController < DeviseController
     # Check if a reset_password_token is provided in the request
     def assert_reset_token_passed
       if params[:reset_password_token].blank?
-        set_flash_message(:error, :no_token)
+        set_flash_message(:alert, :no_token)
         redirect_to new_session_path(resource_name)
       end
     end