fix(package): update @google-cloud/pubsub to version 0.25.0

Closes #15

Author: greenkeeper[bot]

package.json

@@ -35,7 +35,7 @@
         "nkc-pubsub-sink": "bin/nkc-pubsub-sink.js"
     },
     "dependencies": {
-        "@google-cloud/pubsub": "^0.20.0",
+        "@google-cloud/pubsub": "^0.25.0",
         "async": "^2.6.1",
         "kafka-connect": "^3.5.1"
     },