fix(deps): update dependency @google-cloud/promisify to ^0.4.0 (#328)

Author: renovate[bot]

packages/google-cloud-vision/package.json

@@ -42,7 +42,7 @@
     "predocs-test": "npm run docs"
   },
   "dependencies": {
-    "@google-cloud/promisify": "^0.3.0",
+    "@google-cloud/promisify": "^0.4.0",
     "google-gax": "^0.25.0",
     "is": "^3.2.1",
     "lodash.merge": "^4.6.1",