replace sass-mixins reference with bourbon reference

README.md

@@ -45,7 +45,7 @@ If you use Sass in your application, the flutie stylesheets are also available a
 
 You'll want to import flutie before any of your own styles so that you can do things like extend your classes with flutie classes.
 
-We also have a [Sass-Mixins gem](https://github.com/thoughtbot/sass-mixins) available, which extends flutie with a set of vanilla sass mixins.
+We also have a [Bourbon](https://github.com/thoughtbot/bourbon) gem available, which can be used to extend flutie with a set of vanilla sass mixins.
 
 ### Custom Styles
 

app/assets/stylesheets/sass/flutie/flutie.scss

@@ -1,10 +1,9 @@
-// Optional import of sass mixins. See read me for instructions.
-// @import 'sass-mixins/mixins';
+// Optional import of sass mixins from bourbon. See read me for instructions.
+// @import 'bourbon/bourbon';
 @import 'reset';
 @import 'defaults';
 @import 'type';
 @import 'forms';
 @import 'tables';
 @import 'lists';
 @import 'screen';
-