fix it's/its usage in app-spec.md

app-spec.md

@@ -96,9 +96,9 @@ This checkbox toggles all the todos to the same state as itself. Make sure to cl
 
 A todo item has three possible interactions:
 
-1. Clicking the checkbox marks the todo as complete by updating it's `completed` value and toggling the class `completed` on it's parent `<li>`
+1. Clicking the checkbox marks the todo as complete by updating its `completed` value and toggling the class `completed` on its parent `<li>`
 
-2. Double-clicking the `<label>` activates editing mode, by toggling the `.editing` class on it's `<li>`
+2. Double-clicking the `<label>` activates editing mode, by toggling the `.editing` class on its `<li>`
 
 3. Hovering over the todo shows the remove button (`.destroy`)