Update README.md

Author: flocked

README.md

@@ -171,7 +171,7 @@ An extended `NSCollectionViewDiffableDataSource that provides:
 
   A diffable data source for `NSOutlineView` simliar to `CollectionViewDiffableDataSource`.
 
- Example usage of a data source with a `String` as `ItemIdentifierType`:
+ Example usage of a data source with a String as `ItemIdentifierType`:
 
  ```swift
     let dataSource = OutlineViewDiffableDataSource<String>(outlineView: outlineView, cellRegistration: cellRegistration)