Add cats branch to the documentation dropdown
Add cats branch to the documentation dropdown

Refs #1002

aeons/http4s,ChristopherDavenport/http4s,ZizhengTai/http4s,ChristopherDavenport/http4s,aeons/http4s,ChristopherDavenport/http4s,ZizhengTai/http4s,rossabaker/http4s,reactormonk/http4s,rossabaker/http4s,ZizhengTai/http4s,http4s/http4s,reactormonk/http4s,aeons/http4s,reactormonk/http4s