chore(package): update bunyan to version 1.8.1

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -35,7 +35,7 @@
     "test": "make test"
   },
   "devDependencies": {
-    "bunyan": "^1.5.1",
+    "bunyan": "^1.8.1",
     "chai": "^3.4.1",
     "coveralls": "^2.11.4",
     "eslint": "^2.5.0",