Fix a couple minor bugs/typos in pub.

sdk/lib/_internal/pub/lib/src/executable.dart

Index: sdk/lib/_internal/pub/lib/src/executable.dart
diff --git a/sdk/lib/_internal/pub/lib/src/executable.dart b/sdk/lib/_internal/pub/lib/src/executable.dart
index f689572268dc81e794e3945aee2d16a9c85974ea..38105925f88befd4f655776caada5d51c17d5710 100644
--- a/sdk/lib/_internal/pub/lib/src/executable.dart
+++ b/sdk/lib/_internal/pub/lib/src/executable.dart
@@ -118,7 +118,7 @@ Future<int> runExecutable(Entrypoint entrypoint, String package,
     // Get the URL of the executable, relative to the server's root directory.
     var relativePath = p.url.relative(assetPath,
         from: p.url.joinAll(p.split(server.rootDirectory)));
-    vmArgs.add('bin/css.dart');
+    vmArgs.add(server.url.resolve(relativePath).toString());
     vmArgs.addAll(args);
 
     var process = await Process.start(Platform.executable, vmArgs);