[ package:dds ] Add missing package:shelf_static dependency in

pubspec.yaml

Change-Id: Ifd7954d66bd8af2f74d5e718d2dc6f5ccc1f738f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/154564
Reviewed-by: Zichang Guo <[email protected]>

Author: bkonyi

pkg/dds/pubspec.yaml

@@ -17,6 +17,7 @@ dependencies:
   pedantic: ^1.7.0
   shelf: ^0.7.5
   shelf_proxy: ^0.1.0+7
+  shelf_static: ^0.2.8
   shelf_web_socket: ^0.2.3
   sse: ^3.5.0
   stream_channel: ^2.0.0