update devguide

Author: markzegarelli

devguide.md

@@ -4,7 +4,7 @@ The contents of this guide will help you get up and running with the Segment Doc
 
 ## Local development with `ruby` and `node`, without Config API
 
-If using OSX:
+If using MacOS:
   * Install command line tools, `xcode-select --install`
   * Install `Ruby` >= 2.3.0 https://www.ruby-lang.org/en/documentation/installation/
   * Ensure you're running `RubyGems` >= 2.5.0 by running `gem update --system` followed by `gem --version`