Fix ios 9 crash#25

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petropavel13 wants to merge 3 commits intomokagio:masterfrom

petropavel13:fix_ios_9_crash

Commits on Dec 7, 2017

fix iOS 9 crash (https://github.com/mokagio/UICollectionViewLeftAlignedLayout/issues/9)
petropavel13
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Commits on Dec 11, 2017

apply fix only for iOS < 10.0
petropavel13
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Commits on Jul 7, 2018

use @available check
petropavel13
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