fix: upgrade dockerfile-ast from 0.2.1 to 0.5.0

Snyk has created this PR to upgrade dockerfile-ast from 0.2.1 to 0.5.0.

See this package in npm:
https://www.npmjs.com/package/dockerfile-ast

See this project in Snyk:
https://app.snyk.io/org/team-mycelium/project/027df8a9-42d7-4eef-8da8-ca99e88205e1?utm_source=github&utm_medium=referral&page=upgrade-pr

package.json

@@ -38,7 +38,7 @@
     "chalk": "^2.4.2",
     "debug": "^4.1.1",
     "docker-modem": "3.0.3",
-    "dockerfile-ast": "0.2.1",
+    "dockerfile-ast": "0.5.0",
     "elfy": "^1.0.0",
     "event-loop-spinner": "^2.0.0",
     "gunzip-maybe": "^1.4.2",