fix for inherited not supporting subclassing

the arg of inherited is a subclass of the current class, not (just) a ::Class

core/class.rbs

@@ -149,7 +149,7 @@ class Class < Module
   #     New subclass: Bar
   #     New subclass: Baz
   #
-  def inherited: (Class arg0) -> untyped
+  def inherited: (instance arg0) -> untyped
 
   # <!--
   #   rdoc-file=object.c