Temporarily force pub to use dart2js old frontend (#1828)

diff --git a/lib/src/dart.dart b/lib/src/dart.dart
index 2dec254..f673858 100644
--- a/lib/src/dart.dart
+++ b/lib/src/dart.dart
@@ -89,6 +89,7 @@
   if (platformBinaries != null) {
     options.add('--platform-binaries=$platformBinaries');
   }
+  options.add('--use-old-frontend');
 
   var sourceUrl = p.toUri(entrypoint);
   options.add("--out=$sourceUrl.js");