Build: update yargs to version 7.0.1 (#91)

https://greenkeeper.io/

Author: greenkeeper[bot]

package.json

@@ -76,7 +76,7 @@
     "watchify": "^3.7.0",
     "webpack": "^2.2.1",
     "webpack-stream": "^3.2.0",
-    "yargs": "^6.6.0"
+    "yargs": "^7.0.1"
   },
   "browser": {
     "crypto": false