fix(AdaptiveQuality): prevent flickering on Unity 5.4.2
fix(AdaptiveQuality): prevent flickering on Unity 5.4.2

Whenever the render scale is changed the old frame is visible for some
time, looking like flickering when `AdaptiveQuality` is enabled. The
fix is to change the render scale in `LateUpdate` on Unity 5.4.2, too.

TMaloteaux/SteamVR_Unity_Toolkit,thestonefox/VRTK,Fulby/VRTK,pargee/SteamVR_Unity_Toolkit,Innoactive/IA-unity-VR-toolkit-VRTK,nmccarty/htvr,mattboy64/SteamVR_Unity_Toolkit,virror/VRTK,thestonefox/SteamVR_Unity_Toolkit,red-horizon/VRTK,gpvigano/SteamVR_Unity_Toolkit,gpvigano/VRTK,gomez-addams/SteamVR_Unity_Toolkit,adamjweaver/VRTK