use vm github repo in package.json

package.json

@@ -22,7 +22,7 @@
     "ethereumjs-block": "^1.6.0",
     "ethereumjs-tx": "^1.3.3",
     "ethereumjs-util": "^5.1.2",
-    "ethereumjs-vm": "^2.1.0",
+    "ethereumjs-vm": "https://github.com/ethereumjs/ethereumjs-vm",
     "execr": "^1.0.1",
     "exorcist": "^0.4.0",
     "fast-async": "^6.1.2",