Fix link to the Node.js Cloud Run sample readme (#1498)

- [x] Point to the master branch readme file

Author: geshan

run/pubsub/README.md

@@ -4,11 +4,11 @@ This sample shows how to create a service that processes Pub/Sub messages.
 
 Use it with the [Cloud Pub/Sub with Cloud Run tutorial](http://cloud.google.com/run/docs/tutorials/pubsub).
 
-For more details on how to work with this sample read the [Google Cloud Run Node.js Samples README](https://github.com/GoogleCloudPlatform/nodejs-docs-samples/run).
+For more details on how to work with this sample read the [Google Cloud Run Node.js Samples README](https://github.com/GoogleCloudPlatform/nodejs-docs-samples/tree/master/run).
 
 ## Dependencies
 
 * **express**: Web server framework.
 * **body-parser**: express middleware for request payload processing.
 * **mocha**: [development] Test running framework.
-* **supertest**: [development] HTTP assertion test client.
+* **supertest**: [development] HTTP assertion test client.