Merge pull request #541 from bradfitz/docs

Update Server.Stop docs per code review comments from grpc/grpc-go#540
diff --git a/server.go b/server.go
index 19a002a..bcd6196 100644
--- a/server.go
+++ b/server.go
@@ -594,9 +594,11 @@
 	}
 }
 
-// Stop stops the gRPC server. It immediately closes all open connections and listeners. It cancels all
-// active RPCs on server side and the corresponding pending RPCs on client side will get notified by
-// connection errors.
+// Stop stops the gRPC server. It immediately closes all open
+// connections and listeners.
+// It cancels all active RPCs on the server side and the corresponding
+// pending RPCs on the client side will get notified by connection
+// errors.
 func (s *Server) Stop() {
 	s.mu.Lock()
 	listeners := s.lis