change OS X to macOS in Readme

changed OS X to macOS

Author: himalayanelixir

Readme.md

@@ -23,7 +23,7 @@ For detailed installation information, see the [wiki](https://github.com/Automat
 
 OS | Command
 ----- | -----
-OS X | Using [Homebrew](https://brew.sh/):<br/>`brew install pkg-config cairo pango libpng jpeg giflib librsvg pixman`
+macOS | Using [Homebrew](https://brew.sh/):<br/>`brew install pkg-config cairo pango libpng jpeg giflib librsvg pixman`
 Ubuntu | `sudo apt-get install build-essential libcairo2-dev libpango1.0-dev libjpeg-dev libgif-dev librsvg2-dev`
 Fedora | `sudo yum install gcc-c++ cairo-devel pango-devel libjpeg-turbo-devel giflib-devel`
 Solaris | `pkgin install cairo pango pkg-config xproto renderproto kbproto xextproto`