Add Formula for aptly 0.7.1

Summary:
Add Formula for aptly 0.7.1. Aptly is an apt repository package manager.

Test Plan:
brew install aptly
aptly version
brew uninstall aptly
Please read the [Ruby Style Guide](https://github.com/styleguide/ruby) and update this pull request's changes to conform to it (i.e. use double-quotes everywhere) Thanks!