Add `topics` to `pubspec.yaml` (dart-lang/web_socket_channel#362)

pkgs/web_socket_channel/pubspec.yaml

diff --git a/pkgs/web_socket_channel/pubspec.yaml b/pkgs/web_socket_channel/pubspec.yaml
index b745d73..3b65640 100644
--- a/pkgs/web_socket_channel/pubspec.yaml
+++ b/pkgs/web_socket_channel/pubspec.yaml
@@ -19,3 +19,7 @@
 dev_dependencies:
   dart_flutter_team_lints: ^3.0.0
   test: ^1.25.2
+
+topics:
+ - web
+ - http