Fix a couple minor bugs/typos in pub.

sdk/lib/_internal/pub/lib/src/barback/asset_environment.dart

Index: sdk/lib/_internal/pub/lib/src/barback/asset_environment.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/asset_environment.dart b/sdk/lib/_internal/pub/lib/src/barback/asset_environment.dart
index 634c3fcf9aa243c1520abd85ef60555107466aec..197f93b6237a4b3d42775be1fdf8dbacd2f5a929 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/asset_environment.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/asset_environment.dart
@@ -508,7 +508,7 @@ class AssetEnvironment {
       });
 
       await _withStreamErrors(() async {
-        return log.progress("Loading transformers", () {
+        return log.progress("Loading transformers", () async {
           await loadAllTransformers(this, transformerServer,
               entrypoints: entrypoints);
           transformerServer.close();