Update some dev dependencies

Author: realityking

package.json

@@ -30,9 +30,9 @@
     "xxhashjs": "^0.2.1"
   },
   "devDependencies": {
-    "chai": "^3.5.0",
+    "chai": "^4.1.2",
     "eslint": "^3.16.1",
-    "mocha": "^3.2.0",
+    "mocha": "^5.2.0",
     "npmpub": "^3.0.1",
     "postcss-import": "^10.0.0"
   },