fix script constructor array check

src/script.js

@@ -6,7 +6,7 @@ var network = require('./network');
 
 var Script = function(data) {
     this.buffer = data || [];
-    if(!Array.isArray(data)) {
+    if(!Array.isArray(this.buffer)) {
       throw new Error('expect Script to be initialized with Array, but got ' + data)
     }
     this.parse();