Update MIGRATION.md

Author: aksonov

docs/MIGRATION.md

@@ -1,7 +1,7 @@
 # Migrating from 2.x
 
 ## Breaking changes comparing with 2.x version:
-- React Native 0.22 is required
+- React Native 0.26 is required
 - `Router` is root container now and should not be nested. For nested scenes you should use `Scene` element
 - `Route` became `Scene`, now unique `key` attribute is required for each scene (it was `name` attribute before)
 - Define all your scenes on top-level, not within `Router` as before (see Example)
@@ -10,4 +10,4 @@
 - Custom scene renderers are used instead of 'custom' types (like 'modal'), so 'modal' scenes are pushed as usual, but custom renderer will render them as popup. No `dismiss`, just usual `pop` to close such popups.
 - No old navigator.sceneConfig support (instead the component uses React Native NavigationAnimatedView for better transitions)
 - No onPush/onPop/etc handlers because they are not needed now. If navigation state is changed, container will be re-rendered with changed navigationState property, see `Modal` as Example.
-- No header/footer properties are supported for Scene currently - you may include them into Scene component.
+- No header/footer properties are supported for Scene currently - you may include them into Scene component.