add reference to upstream grpc bug

Author: Michal Witkowski

README.md

@@ -36,7 +36,7 @@ proxy.Server(boundListener)
 
 This is *alpha* software, written as a proof of concept. It has been integration-tested, but please expect bugs.
 
-The current implementation depends on a public interface to `ClientConn.PickTransport`, which hopefully will be upstreamed.
+The current implementation depends on a public interface to `ClientConn.Picker()`, which hopefully will be upstreamed in [grpc-go#397](https://github.com/grpc/grpc-go/pull/397).
 
 
 ## Contributors
@@ -50,4 +50,4 @@ Names in no particular order:
 `grpc-proxy` is released under the Apache 2.0 license. See [LICENSE.txt](https://github.com/spf13/mwitkow-io/blob/grpcproxy/LICENSE.txt).
 
 
-Part of the main server loop are lifted from the [grpc-go](https://github.com/grpc/grpc-go) `Server`, which is copyrighted Google Inc. and licensed under MIT license.
+Part of the main server loop are lifted from the [grpc-go](https://github.com/grpc/grpc-go) `Server`, which is copyrighted Google Inc. and licensed under MIT license.