make field be final

Author: jasonjiang9527

src/main/java/io/appium/java_client/service/local/AppiumDriverLocalService.java

@@ -411,7 +411,7 @@ static Slf4jLogMessageContext parseSlf4jContextFromLogMessage(String logMessage)
     public void addLogMessageConsumer(Consumer<String> consumer) {
         checkNotNull(consumer, "consumer parameter is NULL!");
         addOutPutStream(new OutputStream() {
-            private ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+            private final ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
 
             @Override
             public void write(int chr) {