Fixes #237, Right utility buttons don't work properly on iOS 8

This fixes button width not being set correctly in some cases on iOS 8. Fixes #237

On iOS 8, just calling `[self layoutIfNeeded]` after setting the utility buttons appears to be insufficient. The actual buttonsView still has a width of 0 after setting the constant on the width constraint. Explicitly calling `layoutIfNeeded` on the buttonsView fixes this problem.