chore(package): update mocha to version 6.1.1

Closes #25

Author: greenkeeper[bot]

package.json

@@ -38,7 +38,7 @@
     "fast-memoize": "^2.3.0",
     "lodash.memoize": "^4.1.2",
     "memoize-one": "^3.0.1",
-    "mocha": "^5.2.0",
+    "mocha": "^6.1.1",
     "nyc": "^12.0.1",
     "proxy-polyfill": "^0.3.0",
     "sinon": "^5.0.10",