fix: functions/imagemagick/package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-SEMVER-3247795

Author: snyk-bot

functions/imagemagick/package.json

@@ -15,7 +15,7 @@
     "test": "mocha test/*.test.js --timeout=20000 --exit"
   },
   "dependencies": {
-    "@google-cloud/storage": "^5.0.0",
+    "@google-cloud/storage": "^6.0.0",
     "@google-cloud/vision": "^2.0.0",
     "gm": "^1.23.1"
   },