chore(package): update mocha to version 6.1.1

Closes #47

Author: greenkeeper[bot]

package.json

@@ -12,7 +12,7 @@
     "codecov": "^3.0.2",
     "eslint": "^5.0.0",
     "got": "^9.0.0",
-    "mocha": "^5.2.0",
+    "mocha": "^6.1.1",
     "nyc": "^12.0.2",
     "sinon": "^6.0.1"
   },