fix preamble so example compiles

Author: coke

doc/Language/objects.pod6

@@ -838,7 +838,7 @@ my $p1 = Point.new( x => 10, y => 5 );
 =end code
 
 The following C<BUILD> method is equivalent to the above:
-=begin code :preamble<has $!enc; has $!data>
+=begin code :preamble<has $.x; has $.y>
 submethod BUILD(:$!x, :$!y) {
     # Nothing to do here anymore, the signature binding
     # does all the work for us.