chore(package): update mocha to version 6.1.1

Closes #65

Author: greenkeeper[bot]

package.json

@@ -21,7 +21,7 @@
     "babel-preset-es2015": "^6.16.0",
     "babel-preset-react": "^6.16.0",
     "jsdom": "^11.0.0",
-    "mocha": "^4.0.0",
+    "mocha": "^6.1.1",
     "sinon": "^4.0.0",
     "unexpected": "^10.36.0",
     "unexpected-sinon": "^10.1.1"