Fix typo in README.md (#18)

Author: MaxDesiatov

README.md

@@ -22,7 +22,7 @@
 
 This package give you the ability to observe changes to keyboard state using the `Keyboard` `ObservableObject` type.
 
-It also provides a `KeyboardObservingView` that adjusts it's content to avoid the keyboard, and a `.keyboardObserving()` ViewModifier that adjusts the modified view to avoid the keyboard.
+It also provides a `KeyboardObservingView` that adjusts its content to avoid the keyboard, and a `.keyboardObserving()` ViewModifier that adjusts the modified view to avoid the keyboard.
 
 ![Demo](./images/demo.gif)