fix grammar and terminology (reactjs#178)

Author: levsero

lessons/05-active-links/README.md

@@ -50,7 +50,7 @@ primary navigation links need to know. It's useful to wrap those so you
 don't have to remember what your `activeClassName` or `activeStyle` is
 everywhere.
 
-We will use an spread attribute here, the three dots. It clones our props 
+We will use a spread operator here, the three dots. It clones our props 
 and in this use case it clones `activeClassName` to our desired component for
 us to benefit from.