Update diagnostic on compatibility page to reflect reality

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@107382 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/www/compatibility.html b/www/compatibility.html
index 85133fb..0f8409b 100644
--- a/www/compatibility.html
+++ b/www/compatibility.html
@@ -590,9 +590,8 @@
 downcast.mm:6:3: error: no matching function for call to 'f'
   f(base);
   ^
-downcast.mm:4:6: note: candidate function not viable: cannot convert from base
-      class pointer 'Base *' to derived class pointer 'Derived *' for 1st
-      argument
+downcast.mm:4:6: note: candidate function not viable: cannot convert from
+      superclass 'Base *' to subclass 'Derived *' for 1st argument
 void f(Derived *);
      ^
 </pre>