Do not rely on current public error message

There are slight changes in the error message displayed in the public
error pages across Rails versions. Checking for "We're sorry, but
something went wrong." seems to be the safest option.

features/allow_rescue.feature

@@ -32,8 +32,7 @@ Feature: Allow Cucumber to rescue exceptions
         visit '/posts'
       end
       Then /^I should see the public error page$/ do
-        expect(page).to have_content "We're sorry, but something went wrong. \
-          If you are the application owner check the logs for more information."
+        expect(page).to have_content "We're sorry, but something went wrong."
       end
       """
     And I run `bundle exec rake db:migrate`