Update dependency tslint to v5.20.0 (#213)

Author: renovate-bot

package.json

@@ -52,7 +52,7 @@
     "rimraf": "3.0.0",
     "rollup": "0.67.4",
     "rollup-plugin-copy": "3.1.0",
-    "tslint": "5.18.0",
+    "tslint": "5.20.0",
     "typescript": "3.5.3"
   },
   "lint-staged": {