Revert to iOS SDK 4.2.3

iOS SDK 4.3.0, 4.3.1 and 4.3.2 contain iOS 8 compatibility issues in
landscape orientations that will be addressed in an upcoming update,
currently under development. See this SO change for more details about
Apple’s specific change that affects our landscape webview:
http://stackoverflow.com/questions/24150359/is-uiscreen-mainscreen-bound
s-size-becoming-orientation-dependent-in-ios8