C4 mostafahassaan c4 s09 unfollow word

issue #175 @zoheiry @m0hamed @nourhanZ @NourhanMohamed 

Files changed:
app/views/followed/list_followed.html.erb
app/controllers/follow/follow_controller
=>unfollow
app/models/developer.rb
=>unfollow
spec/features/developers_follow_keywords_spec.rb