chore(gitignore): add .agignore
chore(gitignore): add .agignore

I use a .agignore file to skip the build directory and some other files
while searching using Ag (see
https://github.com/ggreer/the_silver_searcher).

ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js