chore(package): update mocha to version 5.2.0

Closes #6

Author: greenkeeper[bot]

package.json

@@ -22,7 +22,7 @@
     "chai": "^4.0.2",
     "gl": "^4.0.2",
     "http-server": "^0.10.0",
-    "mocha": "^3.2.0",
+    "mocha": "^5.2.0",
     "pngjs": "^3.0.0"
   },
   "dependencies": {