Add curly that was missed in a conflict fix

Unfortunately, this shows that there are two different opinions
about what the method !get_default_candidate means.  I have
insufficient fu to fix that one.

src/Perl6/Metamodel/ParametricRoleGroupHOW.nqp

@@ -214,6 +214,7 @@ class Perl6::Metamodel::ParametricRoleGroupHOW
     method WHY() {
         my $c := self.'!get_default_candidate'();
         $c.HOW.WHY
+    }
 
     method language-revision($obj) {
         my $c := self.'!get_default_candidate'($obj);