Fix pjax on iOS Simulator

The iOS 8.0 simulator on Mavericks contains the following in its
user-agent string: "iPhone; CPU iPhone OS 10_9_5 like Mac OS X"

The "OS 1" bit gets interpreted by our regex as if it were iOS 1.0 and
thus forcing pjax to be disabled since history manipulation APIs weren't
stable until iOS 5.0.

Fixes #443