消息失败发送提示色改为红色，同时减少间距

lib/home/send_msg_state.dart

@@ -21,12 +21,12 @@ class _SendMsgStateState extends State<SendMsgState> {
    
         if (msg.state == MsgState.SendingFailed) {
           return Padding(
-              padding: EdgeInsets.only(right: 10),
+              padding: EdgeInsets.only(right: 5),
               child: Icon(Icons.error_outline,
-                  size: 12, color: Color(0xFFc0c0c0)));
+                  size: 12, color: Colors.red));
         } else if (msg.state <= MsgState.Sending) {
           return Padding(
-              padding: EdgeInsets.only(right: 10),
+              padding: EdgeInsets.only(right: 5),
               child: Icon(
                   IconData(0xe657, fontFamily: Constants.IconFontFamily),
                   size: 12,