Update .gitignore with stack build files.
Update .gitignore with stack build files.

ajnsit/keter,snoyberg/keter,bermanjosh/keter,andrewthad/keter,telser/keter,bermanjosh/keter,andrewthad/keter,telser/keter,mwotton/keter,creichert/keter,tolysz/keter,mwotton/keter,tolysz/keter,ajnsit/keter,creichert/keter,snoyberg/keter