pubsub: update gapic layer (#1734)

Author: stephenplusplus

packages/pubsub/package.json

@@ -53,7 +53,7 @@
     "@google-cloud/common": "^0.7.0",
     "arrify": "^1.0.0",
     "extend": "^3.0.0",
-    "google-gax": "^0.7.0",
+    "google-gax": "^0.8.1",
     "google-proto-files": "^0.8.0",
     "is": "^3.0.1",
     "modelo": "^4.2.0",