Rename to cross_file

Author: mvanbeusekom

packages/cross_file/lib/x_file.dart renamed to packages/cross_file/lib/cross_file.dart

@@ -9,7 +9,7 @@ import 'dart:html' as html;
 import 'dart:typed_data';
 
 import 'package:flutter_test/flutter_test.dart';
-import 'package:cross_file/x_file.dart';
+import 'package:cross_file/cross_file.dart';
 
 import 'dart:html';
 

packages/cross_file/test/x_file_html_test.dart

@@ -9,7 +9,7 @@ import 'dart:io';
 import 'dart:typed_data';
 
 import 'package:flutter_test/flutter_test.dart';
-import 'package:cross_file/x_file.dart';
+import 'package:cross_file/cross_file.dart';
 
 // Please note that executing this test with command
 // `flutter test test/x_file_io_test.dart` will set the directory