Rename files using lowercase.

Author: cloudwebrtc

lib/protoo_client.dart

@@ -1 +1 @@
-export 'src/Peer.dart';
+export 'src/peer.dart';

lib/src/Message.dart renamed to lib/src/message.dart

@@ -1,6 +1,6 @@
 import 'dart:async';
 import 'package:events2/events2.dart';
-import 'transports/WebSocketTransport.dart' show WebSocketTransport;
+import 'transports/websocket_transport.dart' show WebSocketTransport;
 import 'Message.dart';
 import 'logger.dart' show Logger;