using 2 separate local variables for cap3 deployment args so that roles don't overwrite each other's arguments

Given the following config/schedule.rb:
  every :day, :roles => [:app] do
    command 'touch this'
  end

  every :day, :roles => [:db] do
    command 'touch that'
  end

When I deploy with Capistrano 3, the arguments passed to `whenever --update_crontab` get mixed together because a single variable is being used for each:

DEBUG[78e9452b] Command: cd /my/path/current && ( rvm default do bundle exec whenever --update-crontab MY_CRONTAB --set output=/my/path/shared/log/log.log --roles=app --update-crontab MY_CRONTAB --set output=/my/path/shared/log/log.log --roles=db )
DEBUG[f7255f02] Command: cd /my/path/current && (  rvm default do bundle exec whenever --update-crontab MY_CRONTAB --set output=/my/path/shared/log/log.log --roles=app --update-crontab MY_CRONTAB --set output=/my/path/shared/log/log.log --roles=db )

This PR fixes that by adding an additional local variable