docs: fix `win.isFocusable()` return type
@@ -1776,7 +1776,7 @@ On macOS it does not remove the focus from the window.
#### `win.isFocusable()` _macOS_ _Windows_
-Returns whether the window can be focused.
+Returns `boolean` - Whether the window can be focused.
#### `win.setParentWindow(parent)`