use ethereumjs-vm 2.3.1

package.json

@@ -27,7 +27,7 @@
     "ethereumjs-block": "^1.2.2",
     "ethereumjs-tx": "^1.1.1",
     "ethereumjs-util": "^4.5.0",
-    "ethereumjs-vm": "2.2.2",
+    "ethereumjs-vm": "2.3.1",
     "fast-async": "^6.1.2",
     "http-server": "^0.9.0",
     "nightwatch": "^0.9.5",