chore(package): update mocha to version 6.2.1

Closes #18

Author: greenkeeper[bot]

package.json

@@ -54,7 +54,7 @@
     "eslint-plugin-import": "^2.9.0",
     "istanbul": "^1.1.0-alpha.1",
     "json-stable-stringify": "^1.0.1",
-    "mocha": "^5.0.4",
+    "mocha": "^6.2.1",
     "parse-json": "^4.0.0",
     "rollup": "^0.60.0",
     "rollup-plugin-babel": "^3.0.3",