fix(deps): update dependency google-gax to ^0.26.0 (#583)

Author: renovate[bot]

handwritten/pubsub/package.json

@@ -62,7 +62,7 @@
     "async-each": "^1.0.1",
     "extend": "^3.0.1",
     "google-auth-library": "^3.0.0",
-    "google-gax": "^0.25.0",
+    "google-gax": "^0.26.0",
     "is-stream-ended": "^0.1.4",
     "lodash.merge": "^4.6.0",
     "lodash.snakecase": "^4.1.1",