Make tokenizer_data_gen.php compatible with older PHP

Our PHP requirement is currently PHP 7.1, so don't use flexible
heredoc.

Author: nikic

ext/tokenizer/tokenizer_data_gen.php

@@ -10,7 +10,8 @@
 
 Please, generate the PHP parser files by scripts/dev/genfiles
 or by running the ./configure build step.
-ERROR);
+ERROR
+    );
     exit(1);
 }