Fixed a typo.

Author: ChrisGrant

README.md

@@ -323,7 +323,7 @@ UIApplication.sharedApplication.delegate;
 
 ## Literals
 
-`NSString`, `NSDictionary`, `NSArray`, and `NSNumber` literals should be used whenever creating immutable instances of those objects. Pay special care that `nil` values not be passed into `NSArray` and `NSDictionary` literals, as this will cause a crash.
+`NSString`, `NSDictionary`, `NSArray`, and `NSNumber` literals should be used whenever creating immutable instances of those objects. Pay special care that `nil` values can not be passed into `NSArray` and `NSDictionary` literals, as this will cause a crash.
 
 **Preferred:**