Pin url_launcher package to prevent major version upgrade (#13952)

* Pin url_launcher to 1.0.3

* Commit results of 'bin/flutter update-packages --force-upgrade'

* Added TODO

examples/flutter_gallery/pubspec.yaml

@@ -7,7 +7,7 @@ dependencies:
   intl: 0.15.2
   connectivity: 0.2.0
   string_scanner: 1.0.2
-  url_launcher: 2.0.0
+  url_launcher: 1.0.3
   cupertino_icons: 0.1.1
   video_player: 0.0.7
 

packages/flutter_tools/lib/src/commands/update_packages.dart

@@ -30,6 +30,10 @@ const Map<String, String> _kManuallyPinnedDependencies = const <String, String>{
   // https://github.com/dart-lang/sdk/issues/31442
   // TODO(amirh): unpin this.
   'test': '0.12.26',
+  // Major version upgrade to next version(2.0.0) breaks flutter build:
+  // https://github.com/flutter/flutter/issues/13953
+  // TODO(aam): unpin this.
+  'url_launcher': '1.0.3',
   // Add pinned packages here.
 };