Fix milestone reopen

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/services/milestones/reopen_service.rb

 module Milestones
   class ReopenService < Milestones::BaseService
     def execute(milestone)
-      if milestone.reopen
+      if milestone.activate
         event_service.reopen_milestone(milestone, current_user)
       end

app/services/milestones/update_service.rb

 module Milestones
   class UpdateService < Milestones::BaseService
     def execute(milestone)
-      state = params.delete('state_event')
+      state = params.delete('state_event') || params.delete(:state_event)
       case state
-      when 'reopen'
+      when 'activate'
         Milestones::ReopenService.new(project, current_user, {}).execute(milestone)
       when 'close'
         Milestones::CloseService.new(project, current_user, {}).execute(milestone)