updates esprima to 4.0

requires npm installed esprima in structured.js

Author: ianmunrobot

package.json

@@ -23,7 +23,7 @@
     "url": "https://github.com/Khan/structuredjs/issues"
   },
   "dependencies": {
-    "esprima": "~2.7",
+    "esprima": "~4.0.0",
     "underscore": "~1.5.1",
     "react": "^0.11.1",
     "escodegen": "^1.3.3"

structured.js

@@ -20,7 +20,7 @@
 
     if (typeof module !== "undefined" && module.exports) {
         exports = module.exports = {};
-        esprima = require("./external/esprima.js");
+        esprima = require("esprima");
         _ = require("underscore");
     } else {
         exports = this.Structured = {};