Upgrade to mocha 6

Author: Chasen Le Hara

package.json

@@ -28,7 +28,7 @@
   "devDependencies": {
     "bit-docs-generate-html": "^0.1.0",
     "connect": "^2.14.4",
-    "mocha": "^2.5.3",
+    "mocha": "^6.0.2",
     "zombie": "^4.3.0"
   }
 }