chore(deps): update dependency mocha to v6

Author: renovate-bot

package.json

@@ -61,7 +61,7 @@
     "eslint-plugin-ember": "6.2.0",
     "eslint-plugin-node": "8.0.1",
     "loader.js": "4.7.0",
-    "mocha": "5.2.0",
+    "mocha": "6.0.2",
     "qunit-dom": "0.8.4",
     "testdouble": "3.11.0"
   },