chore(package): update mocha to version 6.2.2

Closes #37

Author: greenkeeper[bot]

package.json

@@ -38,7 +38,7 @@
     "eslint": "^4.1.0",
     "istanbul": "^0.4.5",
     "jsdom": "^11.0.0",
-    "mocha": "^5.0.0",
+    "mocha": "^6.2.2",
     "nyc": "^12.0.2",
     "preact": "^8.1.0",
     "rollup": "^0.59.0",