Update README to specify correct ctags library

Universal Ctags was added in thoughtbot#503 but the README wasn't updated so it
still refers to the Exuberant Ctags.

README.md

@@ -73,7 +73,7 @@ macOS tools:
 
 Unix tools:
 
-* [Exuberant Ctags] for indexing files for vim tab completion
+* [Universal Ctags] for indexing files for vim tab completion
 * [Git] for version control
 * [OpenSSL] for Transport Layer Security (TLS)
 * [RCM] for managing company and personal dotfiles
@@ -82,7 +82,7 @@ Unix tools:
 * [Watchman] for watching for filesystem events
 * [Zsh] as your shell
 
-[Exuberant Ctags]: http://ctags.sourceforge.net/
+[Universal Ctags]: https://ctags.io/
 [Git]: https://git-scm.com/
 [OpenSSL]: https://www.openssl.org/
 [RCM]: https://github.com/thoughtbot/rcm