chore(package): update mocha to version 6.0.0 (#340)

Author: greenkeeper[bot]

package.json

@@ -49,7 +49,7 @@
     "codeclimate-test-reporter": "^0.5.0",
     "coveralls": "^3.0.0",
     "eslint": "^5.6.0",
-    "mocha": "^5.0.0",
+    "mocha": "^6.0.0",
     "nock": "^10.0.0",
     "nyc": "^13.0.1",
     "proxyquire": "^2.0.0",