Fix inherit from deprecated `ActionView::Template::Handlers::Erubis`

There are some classes inherit from `ActionView::Template::Handlers::Erubis`.
(ex. https://github.com/haml/haml/blob/4.0.7/lib/haml/helpers/safe_erubis_template.rb#L3)

```
Class.new(ActionView::Template::Handlers::Erubis)
# => TypeError: superclass must be a Class (ActiveSupport::Deprecation::DeprecatedConstantProxy given)
```

1 files changed, 2 insertions, 0 deletions

diff --git a/actionview/test/template/erb/deprecated_erubis_implementation_test.rb b/actionview/test/template/erb/deprecated_erubis_implementation_test.rb
index 4a130e6c33..aaf99f85c0 100644
--- a/actionview/test/template/erb/deprecated_erubis_implementation_test.rb
+++ b/actionview/test/template/erb/deprecated_erubis_implementation_test.rb
@@ -5,6 +5,8 @@ module ERBTest
     test "Erubis implementation is deprecated" do
       assert_deprecated "ActionView::Template::Handlers::Erubis is deprecated and will be removed from Rails 5.2. Switch to ActionView::Template::Handlers::ERB::Erubi instead." do
         assert_equal "ActionView::Template::Handlers::ERB::Erubis", ActionView::Template::Handlers::Erubis.to_s
+
+        assert_nothing_raised { Class.new(ActionView::Template::Handlers::Erubis) }
       end
     end
   end