fixed

[iOS SDK] Fixed a minor bug

we improved the performance of the infinite scroll.

PXLGridView.swift is improved.
no need for changing the app side codes
For you to check this change in the demo app, you can open the demo app and tab '[List type] Two-column' menu.

for more information, please visit https://github.com/pixlee/pixlee-ios-sdk/releases/tag/2.5.3