make package private

Author: VinayGuthal

firebase-messaging/src/main/java/com/google/firebase/messaging/ByteStreams.java

@@ -25,7 +25,7 @@
 import java.util.Queue;
 
 /** @hide */
-public final class ByteStreams {
+final class ByteStreams {
 
  private static final int BUFFER_SIZE = 8192;