Fix crash on iPad Air 3rd gen. (only !?)

[Quimoune]

Hello,

I've got an issue from several weeks but only on iPad Air (3rd gen.). I didn't have time to know exactly what causing this crash.. but I made a small piece of code to prevent it. I won't make a PR but if you could check and see this modification :

In JZWeekViewFlowLayout.swift in line 587 : New line => let availableRange = CGFloat(floorf(Float(adjustedRange.upperBound)))...CGFloat(ceilf(Float(lastAvailableRange.upperBound)))

Otherwise your framework is awesome !! Thanks.