fix(package): update google-gax to version 0.16.0 (#153)

Author: greenkeeper[bot]

package.json

@@ -57,7 +57,7 @@
     "deep-equal": "^1.0.1",
     "extend": "^3.0.1",
     "functional-red-black-tree": "^1.0.1",
-    "google-gax": "^0.15.0",
+    "google-gax": "^0.16.0",
     "is": "^3.2.1",
     "safe-buffer": "^5.1.1",
     "through2": "^2.0.3"