chore(package): update mocha to version 6.2.1

Closes #56

Author: greenkeeper[bot]

package.json

@@ -29,7 +29,7 @@
     "chai": "^4.1.2",
     "eslint": "^4.11.0",
     "eslint-config-pedant": "^1.0.0",
-    "mocha": "^5.0.0",
+    "mocha": "^6.2.1",
     "nyc": "^11.3.0",
     "proxyquire": "^1.8.0",
     "sinon": "^4.1.2",