minor mistake fix

This method was referred to as the second method, which was confusing since the method before it was also referred to as the second method. Removed the ordinal; just use the name, for future-proofing.

doc/Language/classtut.pod6

@@ -269,7 +269,7 @@ The method itself takes the passed parameter – which must be an instance of
 the C<Task> class – and C<push>es it onto the invocant's C<@!dependencies>
 attribute.
 
-The second method contains the main logic of the dependency handler:
+The C<perform> method contains the main logic of the dependency handler:
 
     method perform() {
         unless $!done {