upgrade(@google-cloud/storage): ^5.7.0 (#157)

This is to upgrade the vulnerable `axios` dependency. The latest version has the following breaking changes which are all okay:

- automatically detect contentType if not provided (googleapis/nodejs-storage#1190)
- drop keepAcl parameter in file copy (googleapis/nodejs-storage#1166)
- drop support for node.js 8.x
- allow leading slashes in file name (googleapis/nodejs-storage#820)
- upgrade engines field to >=8.10.0 (googleapis/nodejs-storage#688)

package.json

@@ -20,7 +20,7 @@
     "**/yargs-parser": ">=18.1.2"
   },
   "dependencies": {
-    "@google-cloud/storage": "2.3.4",
+    "@google-cloud/storage": "^5.7.0",
     "@octokit/plugin-retry": "2.2.0",
     "@octokit/rest": "16.35.2",
     "@sentry/node": "4.6.3",