chore(deps): update dependency mocha to v8

Author: renovate-bot

package.json

@@ -59,7 +59,7 @@
     "eslint-plugin-ember": "9.6.0",
     "eslint-plugin-node": "11.1.0",
     "loader.js": "4.7.0",
-    "mocha": "6.2.3",
+    "mocha": "8.2.1",
     "qunit-dom": "1.6.0",
     "testdouble": "3.16.0"
   },