rsync install from Github produces 404 error (deprecated repo).

[jtkiley]

The homebrew-dupes repo has been deprecated, and it's causing the line below to produce an error.

https://github.com/necolas/dotfiles/blob/986157a70a595fdbee540f06a491a68b339a9b00/lib/brew#L57

curl: (22) The requested URL returned error: 404 Not Found
Error: Failure while executing; `/usr/bin/curl -q --show-error --user-agent Homebrew/1.9.2\ \(Macintosh\;\ Intel\ Mac\ OS\ X\ 10.14.2\)\ curl/7.54.0 --fail --progress-bar --location --remote-time --continue-at 0 --output /Users/USERNAME/Library/Caches/Homebrew/Formula/rsync.rb https://raw.github.com/Homebrew/homebrew-dupes/master/rsync.rb` exited with 22. Here's the output:

curl: (22) The requested URL returned error: 404 Not Found

The fix is to point to the homebrew-core repo. PR incoming.