Fixed deprecated method in GRPC Java test.

Change-Id: Iccae8fe9409adbf3cd3013a5cf3368e068175ad3

grpc/tests/JavaGrpcTest.java

@@ -141,7 +141,7 @@ public class JavaGrpcTest {
         channel = ManagedChannelBuilder.forAddress("localhost", port)
                 // Channels are secure by default (via SSL/TLS). For the example we disable TLS to avoid
                 // needing certificates.
-                .usePlaintext(true)
+                .usePlaintext()
                 .directExecutor()
                 .build();
         blockingStub = MonsterStorageGrpc.newBlockingStub(channel);