Update dependency tslint to v5.20.0

Author: renovate-bot

package-lock.json

@@ -47,7 +47,7 @@
     "rollup-plugin-typescript": "1.0.1",
     "should": "13.2.3",
     "ts-node": "8.3.0",
-    "tslint": "5.19.0",
+    "tslint": "5.20.0",
     "tslint-config-prettier": "1.18.0",
     "typedoc": "0.15.0",
     "typescript": "3.5.3",