Assert with a non existent file using Regexp

In the RBX and Ruby the Errno::ENOENT are different.

This patch uses a regexp this way we can handle both platforms.

test/active_model_serializers/test/schema_test.rb

@@ -102,14 +102,14 @@ def test_that_assert_with_a_custom_schema_directory
       end
 
       def test_with_a_non_existent_file
-        message = 'No such file or directory - No Schema file at test/support/schemas/non-existent.json'
+        message = %r{.* - No Schema file at test/support/schemas/non-existent.json}
 
         get :show
 
         error = assert_raises ActiveModelSerializers::Test::Schema::MissingSchema do
           assert_response_schema('non-existent.json')
         end
-        assert_equal(message, error.message)
+        assert_match(message, error.message)
       end
 
       def test_that_raises_with_a_invalid_json_body