chore(package): update mocha to version 6.1.0

Closes #8

Author: greenkeeper[bot]

package.json

@@ -20,7 +20,7 @@
     "yosay": "^2.0.0"
   },
   "devDependencies": {
-    "mocha": "^3.1.2"
+    "mocha": "^6.1.0"
   },
   "license": "MIT",
   "repository": {