Upgraded ethereumjs-util to fix sign message issue

.gitignore

+.idea
 .vscode
 build
 node_modules

package.json

@@ -21,7 +21,7 @@
     "csjs-inject": "^1.0.1",
     "csslint": "^1.0.2",
     "deep-equal": "^1.0.1",
-    "ethereumjs-util": "^5.1.2",
+    "ethereumjs-util": "^6.1.0",
     "execr": "^1.0.1",
     "exorcist": "^0.4.0",
     "fast-async": "6.3.1",