fix(package): update ethereumjs-util to version 7.0.0

Closes #206

Author: greenkeeper[bot]

package.json

@@ -41,7 +41,7 @@
     "commander": "2.19.0",
     "console.table": "0.10.0",
     "dotenv": "6.2.0",
-    "ethereumjs-util": "6.1.0",
+    "ethereumjs-util": "7.0.0",
     "keen-tracking": "4.0.7",
     "lokijs": "1.5.6",
     "moment": "2.23.0",