Adopt cats version convention atop http4sVersion
Adopt cats version convention atop http4sVersion

Fixes #875

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