chore(deps): update dependency tslint to v5.20.1

Author: renovate-bot

package.json

@@ -19,7 +19,7 @@
   },
   "devDependencies": {
     "@types/node": "8.5.7",
-    "tslint": "5.8.0",
+    "tslint": "5.20.1",
     "typescript": "2.6.2"
   }
 }