Use code block and not a sub in example

.of on sub {} uses Callable.of()

Author: zoffixznet

doc/Type/Code.pod6

@@ -67,7 +67,7 @@ Defined as:
 Returns the L<return type constraint|/type/Signature#Constraining_Return_Types>
 of the C<Code>:
 
-    m: say sub () returns Int {}.of
+    m: say -> () --> Int {}.of
     # OUTPUT: (Int)
 
 =head2 method signature