Update type-system.md

Author: andrew-johnson-4

type-system.md

@@ -65,7 +65,7 @@ There is a slight distinction made between standard unification and specializati
 We say that specialization chooses "the most specific" candidate, but what does that really mean?
 We might think that specialization is just the deepest subtype, but that would be wrong.
 
-When we have two candidates such as `x -> x` and it's specialized version `A -> A`, we obviously want to choose the specialized version.
+When we have two candidates such as `x -> x` and its specialized version `A -> A`, we obviously want to choose the specialized version.
 However, in standard subtyping relations, the parametric version is the subtype.
 This is because `x -> x` can become a `A -> A`, but `A -> A` cannot become a `x -> x`.
 So something needs to change.