fix code typo that didn't compile.

doc/Language/grammars.pod6

@@ -368,6 +368,7 @@ itself. Note that mutating an attribute from within a method called in a token
 will I<only modify the attribute for that token's own match object>! Grammar
 attributes can be accessed in the match returned after parsing if made public:
 
+=begin code
     grammar HTTPRequest {
         has Bool $.invalid;
 
@@ -400,14 +401,15 @@ attributes can be accessed in the match returned after parsing if made public:
         }
     }
 
-    my $header = "MEOWS / HTTP/1.1\r\nHost: docs.perl6.org\r\nsup lol\r\n\r\n";.
+    my $header = "MEOWS / HTTP/1.1\r\nHost: docs.perl6.org\r\nsup lol\r\n\r\n";
     my $/ = HTTPRequest.parse($header);
     say $<type>.invalid;
     # OUTPUT: True
     say $<path>.invalid;
     # OUTPUT: (Bool)
     say $<field>».invalid;
     # OUTPUT: [(Bool) True]
+=end code
 
 X<|Actions>
 =head1 Action objects