\Z -> \z

Here we want end of string, no optional newlines are to
be expected, so \z is more concise.

activesupport/lib/active_support/core_ext/module/introspection.rb

@@ -10,7 +10,7 @@ def module_parent_name
     if defined?(@parent_name)
       @parent_name
     else
-      parent_name = name =~ /::[^:]+\Z/ ? -$` : nil
+      parent_name = name =~ /::[^:]+\z/ ? -$` : nil
       @parent_name = parent_name unless frozen?
       parent_name
     end