Fix @VERSION substitution in build-time preprocessing

The code didn't work properly when multiple @VERSION strings were
present in a preprocessed file.

Jakefile

@@ -99,7 +99,7 @@ function preprocess(file) {
     } else {
       return line;
     }
-  }).join("\n").replace("@VERSION", PEGJS_VERSION);
+  }).join("\n").replace(/@VERSION/g, PEGJS_VERSION);
 }
 
 desc("Generate the grammar parser");