fix(DOCUMENTATION): amend spelling error
fix(DOCUMENTATION): amend spelling error

The word `Highlight` was spelt incorrectly in the
Touch Interactions section.
gpvigano/VRTK,Blueteak/SteamVR_Unity_Toolkit,mbbmbbmm/SteamVR_Unity_Toolkit,Fulby/VRTK,TMaloteaux/SteamVR_Unity_Toolkit,red-horizon/VRTK,virror/VRTK,gpvigano/SteamVR_Unity_Toolkit,Innoactive/IA-unity-VR-toolkit-VRTK,pargee/SteamVR_Unity_Toolkit,mattboy64/SteamVR_Unity_Toolkit,phr00t/SteamVR_Unity_Toolkit,gomez-addams/SteamVR_Unity_Toolkit,jcrombez/SteamVR_Unity_Toolkit,nmccarty/htvr,thestonefox/SteamVR_Unity_Toolkit,thestonefox/VRTK,adamjweaver/VRTK,mimminito/SteamVR_Unity_Toolkit