Increases timeout of client_streaming test to 4s

src/objective-c/examples/Sample/SampleTests/RemoteProtoTests.m

@@ -127,7 +127,7 @@
     [expectation fulfill];
   }];
 
-  [self waitForExpectationsWithTimeout:2. handler:nil];
+  [self waitForExpectationsWithTimeout:4. handler:nil];
 }
 
 @end