Update dependency del to v5

Author: renovate-bot

package-lock.json

@@ -34,7 +34,7 @@
     "amp-toolbox-optimizer": "^0.5.3",
     "amphtml-validator": "1.0.23",
     "bignumber.js": "8.1.1",
-    "del": "4.1.1",
+    "del": "5.0.0",
     "domelementtype": "1.3.1",
     "eslint": "5.16.0",
     "eslint-config-google": "^0.12.0",