chore(package): update mocha to version 6.1.1

Closes #3

Author: greenkeeper[bot]

package.json

@@ -13,7 +13,7 @@
     "chai-spies": "^1.0.0",
     "http2-debug": "1.2.1",
     "istanbul": "0.4.5",
-    "mocha": "^5.1.1"
+    "mocha": "^6.1.1"
   },
   "keywords": [
     "http2",