Update ISSUE_TEMPLATE.md
Update ISSUE_TEMPLATE.md

Now that ember-cli supports using yarn, it is likely that more issues will come through with regards to yarn usage and integration with ember-cli. Because of that, we should ask users to include their yarn version number in issue reports. If they are not using yarn, we'll simply see a "command not found" message as the last line in the output.
rtablada/ember-cli,ef4/ember-cli,trentmwillis/ember-cli,cibernox/ember-cli,akatov/ember-cli,balinterdi/ember-cli,ember-cli/ember-cli,sivakumar-kailasam/ember-cli,thoov/ember-cli,jrjohnson/ember-cli,kategengler/ember-cli,kellyselden/ember-cli,raycohen/ember-cli,jgwhite/ember-cli,Turbo87/ember-cli,mike-north/ember-cli,patocallaghan/ember-cli,thoov/ember-cli,pzuraq/ember-cli,gfvcastro/ember-cli,balinterdi/ember-cli,elwayman02/ember-cli,fpauser/ember-cli,gfvcastro/ember-cli,kanongil/ember-cli,patocallaghan/ember-cli,pzuraq/ember-cli,trentmwillis/ember-cli,ef4/ember-cli,elwayman02/ember-cli,sivakumar-kailasam/ember-cli,kellyselden/ember-cli,akatov/ember-cli,pzuraq/ember-cli,mike-north/ember-cli,pzuraq/ember-cli,ember-cli/ember-cli,kanongil/ember-cli,ef4/ember-cli,kanongil/ember-cli,mike-north/ember-cli,fpauser/ember-cli,cibernox/ember-cli,trentmwillis/ember-cli,sivakumar-kailasam/ember-cli,jgwhite/ember-cli,Turbo87/ember-cli,buschtoens/ember-cli,twokul/ember-cli,asakusuma/ember-cli,Turbo87/ember-cli,HeroicEric/ember-cli,mike-north/ember-cli,asakusuma/ember-cli,twokul/ember-cli,akatov/ember-cli,kellyselden/ember-cli,ember-cli/ember-cli,HeroicEric/ember-cli,fpauser/ember-cli,thoov/ember-cli,rtablada/ember-cli,gfvcastro/ember-cli,trentmwillis/ember-cli,kellyselden/ember-cli,fpauser/ember-cli,HeroicEric/ember-cli,twokul/ember-cli,ef4/ember-cli,sivakumar-kailasam/ember-cli,kategengler/ember-cli,buschtoens/ember-cli,cibernox/ember-cli,rtablada/ember-cli,kanongil/ember-cli,thoov/ember-cli,twokul/ember-cli,gfvcastro/ember-cli,patocallaghan/ember-cli,jrjohnson/ember-cli,patocallaghan/ember-cli,raycohen/ember-cli,Turbo87/ember-cli,HeroicEric/ember-cli,rtablada/ember-cli,akatov/ember-cli,jgwhite/ember-cli,jgwhite/ember-cli,cibernox/ember-cli