Fix a minor typo (quii#203)

arrays-and-slices.md

@@ -101,7 +101,7 @@ using `_` [blank identifier](https://golang.org/doc/effective_go.html#blank).
 
 ### Arrays and their type
 
-An interesting property of arrays is the size is encoded in its type. If you try
+An interesting property of arrays is that the size is encoded in its type. If you try
 to pass an `[4]int` into a function that expects `[5]int`, it won't compile.
 They are different types so it's just the same as trying to pass a `string` into
 a function that wants an `int`.