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[rename fixit] Flex alignments

* justifyContent -> mainAxisAlignment
* alignItems -> crossAxisAlignment
* FlexJustifyContent -> MainAxisAlignment
* FlexAlignItems -> CrossAxisAlignment

Fixes #231
A
Adam Barth committed
d5b2e2a01ca983793f2b68886c031f4255e7b606
Parent: 5e1af2f