parse.y: Need to mark the third element of `NODE_HEREDOC`

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60489 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

parse.y

@@ -6640,6 +6640,7 @@ parser_heredoc_identifier(struct parser_params *parser)
     len = lex_p - lex_pbeg;
     lex_goto_eol(parser);
     add_mark_object(lit = STR_NEW(tok(), toklen()));
+    add_mark_object(lex_lastline);
     lex_strterm = rb_node_newnode(NODE_HEREDOC,
 				  lit,			/* nd_lit */
 				  len,			/* nd_nth */