fix typo

README.md

@@ -7,7 +7,7 @@ Flutter is optimized for today's, and tomorrow's, mobile devices. We are
 focused on low-latency input and high frame rates on Android and iOS.
 
 _Flutter is an early-stage open-source project._ We are still missing core
-features like accessibility, text input, localisation, and more. However,
+features like accessibility, text input, localization, and more. However,
 you can build demos and examples today. We hope you try it out and send
 us [feedback](mailto:flutter-dev@googlegroups.com).