refactor subscription_select.js to use ES class syntax
refactor subscription_select.js to use ES class syntax

dplarson/gitlabhq,dreampet/gitlab,iiet/iiet-git,mmkassem/gitlabhq,stoplightio/gitlabhq,jirutka/gitlabhq,iiet/iiet-git,stoplightio/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,t-zuehlsdorff/gitlabhq,mmkassem/gitlabhq,dplarson/gitlabhq,axilleas/gitlabhq,axilleas/gitlabhq,iiet/iiet-git,axilleas/gitlabhq,dreampet/gitlab,dplarson/gitlabhq,jirutka/gitlabhq,mmkassem/gitlabhq,axilleas/gitlabhq,dplarson/gitlabhq,t-zuehlsdorff/gitlabhq,t-zuehlsdorff/gitlabhq,dreampet/gitlab,t-zuehlsdorff/gitlabhq,iiet/iiet-git,jirutka/gitlabhq,stoplightio/gitlabhq,dreampet/gitlab,jirutka/gitlabhq