modify bower.command.list on 'data' to on 'end'
modify bower.command.list on 'data' to on 'end'

I found it can not concat files ,because the `bower.command.list` has not event "data" but "end"
frontday/grunt-bower-concat,onesfreedom/grunt-bower-concat,frontday/grunt-bower-concat,onesfreedom/grunt-bower-concat,AuyaJackie/grunt-bower-concat,Keyes/grunt-bower-concat,mathiber/grunt-bower-concat,alwin-rewedigital/grunt-bower-concat,Keyes/grunt-bower-concat,mathiber/grunt-bower-concat,onesfreedom/grunt-bower-concat,mathiber/grunt-bower-concat,webdev1001/grunt-bower-concat,frontday/grunt-bower-concat,Keyes/grunt-bower-concat,AuyaJackie/grunt-bower-concat,AuyaJackie/grunt-bower-concat,AuyaJackie/grunt-bower-concat,onesfreedom/grunt-bower-concat,Keyes/grunt-bower-concat,webdev1001/grunt-bower-concat,Keyes/grunt-bower-concat,mathiber/grunt-bower-concat,frontday/grunt-bower-concat,mathiber/grunt-bower-concat,webdev1001/grunt-bower-concat,webdev1001/grunt-bower-concat,onesfreedom/grunt-bower-concat,frontday/grunt-bower-concat,AuyaJackie/grunt-bower-concat,sapegin/grunt-bower-concat,webdev1001/grunt-bower-concat