fix(deps): update dependency @google-cloud/promisify to v2 (#417)

Author: renovate-bot

packages/google-cloud-compute/package.json

@@ -39,7 +39,7 @@
     "@google-cloud/common": "^2.3.0",
     "@google-cloud/paginator": "^3.0.0",
     "@google-cloud/projectify": "^1.0.0",
-    "@google-cloud/promisify": "^1.0.0",
+    "@google-cloud/promisify": "^2.0.0",
     "arrify": "^2.0.0",
     "async": "^3.0.0",
     "extend": "^3.0.2",