Update Autoprefixer for iOS 6

Update Autoprefixer for iOS 6. This fixes some bugs with the Align component on iOS 6

Status: **Ready for review**

Reviewers: **@kpeatt**

Ticket: Fixes [#71](https://github.com/mobify/stencil/issues/71), [#72](https://github.com/mobify/stencil/issues/72), [#73](https://github.com/mobify/stencil/issues/73)