[Unity] Update to Unity 6.4.xx, project is not working after 6.2

[PierreFonda3D]

Right now the whole project is deprecated after 6.2

Need to update it to follow new fontionnalities the LTS is 6.4 right now.
The team is currently using 6.0.50f witch is 1 year old (not that old) but is considererd having "security leaks"