Update README.md (#6554)

Minor spelling mistake.

plugins/bgnotify/README.md

@@ -10,7 +10,7 @@ Standalone homepage: [t413/zsh-background-notify](https://github.com/t413/zsh-ba
 
 Just add bgnotify to your plugins list in your `.zshrc`
 
-- On OS X you'll need [terminal-notifer](https://github.com/alloy/terminal-notifier)
+- On OS X you'll need [terminal-notifier](https://github.com/alloy/terminal-notifier)
   * `brew install terminal-notifier` (or `gem install terminal-notifier`)
 - On ubuntu you're already all set!
 - On windows you can use [notifu](http://www.paralint.com/projects/notifu/) or the Cygwin Ports libnotify package