chore(tests): update mocha to the latest version 🚀 (NodeRedis#52)

* chore(package): update mocha to version 6.1.1

* tests: drop Node 4 from travis

Mocha has dropped support for node 4 a few major versions ago.

Co-authored-by: Mike Diarmid <[email protected]>

Author: greenkeeper[bot]

.travis.yml

@@ -9,7 +9,6 @@ addons:
     packages:
     - g++-4.8
 node_js:
-  - "4"
   - "6"
   - "7"
   - "8"

package.json

@@ -41,7 +41,7 @@
     "codeclimate-test-reporter": "^0.5.0",
     "hiredis": "^0.5.0",
     "istanbul": "^0.4.0",
-    "mocha": "^5.0.0",
+    "mocha": "^6.1.1",
     "standard": "^11.0.1"
   },
   "author": "Ruben Bridgewater",