Remove `:github` from install instructions
Remove `:github` from install instructions

The gem is available on rubygem.org. Any reason you would want users to install directly from GitHub?
gregmolnar/activerecord-session_store,maschwenk/activerecord-session_store,rails/activerecord-session_store,Partyista/activerecord-session_store,buntine/activerecord-session_store,maclover7/activerecord-session_store