Merge pull request scala#1006 from IDispose/patch-1

used proper singular. A instead of AN

Author: SethTisue

_tour/variances.md

@@ -147,7 +147,7 @@ abstract class SmallAnimal extends Animal
 case class Mouse(name: String) extends SmallAnimal
 ```
 
-Suppose we're working with functions that accept types of animals, and return the types of food they eat. If we would like a `Cat => SmallAnimal` (because cats eat small animals), but are given a `Animal => Mouse` instead, our program will still work. Intuitively an `Animal => Mouse` will still accept a `Cat` as an argument, because a `Cat` is an `Animal`, and it returns a `Mouse`, which is also an `SmallAnimal`. Since we can safely and invisibly substitute the former for the latter, we can say `Animal => Mouse` is a subtype of `Cat => SmallAnimal`.
+Suppose we're working with functions that accept types of animals, and return the types of food they eat. If we would like a `Cat => SmallAnimal` (because cats eat small animals), but are given a `Animal => Mouse` instead, our program will still work. Intuitively an `Animal => Mouse` will still accept a `Cat` as an argument, because a `Cat` is an `Animal`, and it returns a `Mouse`, which is also a `SmallAnimal`. Since we can safely and invisibly substitute the former for the latter, we can say `Animal => Mouse` is a subtype of `Cat => SmallAnimal`.
 
 ### Comparison With Other Languages