fix: upgrade redis from 3.0.2 to 3.1.2

Snyk has created this PR to upgrade redis from 3.0.2 to 3.1.2.

See this package in npm:
https://www.npmjs.com/package/redis

See this project in Snyk:
https://app.snyk.io/org/klemek/project/81af650f-8c8e-4116-b289-95415c85d8a7?utm_source=github&utm_medium=referral&page=upgrade-pr

package.json

@@ -14,7 +14,7 @@
     "ncp": "^2.0.0",
     "node-prismjs": "^0.1.0",
     "prismjs": "^1.23.0",
-    "redis": "^3.0.2",
+    "redis": "^3.1.2",
     "rss": "^1.2.2",
     "showdown": "^1.9.1"
   },