Add 'which', which sounds better.

Author: gdonald

doc/Language/objects.pod6

@@ -748,7 +748,7 @@ the role that is mixed in.
 Roles can also be mixed into a class using C<is>. However, the semantics of
 C<is> with a role are quite different from those offered by C<does>. With C<is>,
 a class is punned from the role, and then inherited from. Thus, there is no
-flattening composition, and none of the safeties C<does> provides.
+flattening composition, and none of the safeties which C<does> provides.
 
 =begin code
 constant ⲧ = " " xx 4; #Just a ⲧab