Merge pull request h5bp#323 from halfer/master

Remove incorrect apostrophe

Author: darcyclarke

README.md

@@ -64,7 +64,7 @@ This file contains a number of front-end interview questions that can be used wh
 
 #### CSS Questions:
 
-* What is the difference between classes and ID's in CSS?
+* What is the difference between classes and IDs in CSS?
 * What's the difference between "resetting" and "normalizing" CSS? Which would you choose, and why?
 * Describe Floats and how they work.
 * Describe z-index and how stacking context is formed.