fix(deps): update dependency google-gax to ^0.25.0 (#315)

Author: renovate[bot]

package.json

@@ -41,7 +41,7 @@
  },
  "dependencies": {
  "@google-cloud/promisify": "^0.3.0",
- "google-gax": "^0.24.0",
+ "google-gax": "^0.25.0",
  "is": "^3.2.1",
  "lodash.merge": "^4.6.1",
  "protobufjs": "^6.8.6"