chore(package): update mocha to version 6.1.0

Closes #74

Author: greenkeeper[bot]

package.json

@@ -26,7 +26,7 @@
     "babel-core": "^6.26.0",
     "babel-preset-es2015": "^6.24.1",
     "jshint": "^2.9.5",
-    "mocha": "~5.2.0",
+    "mocha": "~6.1.0",
     "nock": "~10.0.0",
     "sinon": "~6.0.1",
     "testen": "^2.2.1"