Gate 1.2 Final Release installer to VS 2015 update 3 final or later

[mjbvz]

#990 and #993 handle the gating of NTVS 1.2 Beta to VS 2015 Update 3 RC.

For the final NTVS 1.2 release, we should gate the NTVS 1.2 installer to VS 2015 Update 3 final instead, once it becomes publicly available.

[mousetraps]

@mjbvz can you update the installer to gate on Update 3 after #1099 goes in?

[mjbvz]

Sure, do you know the version number of VS2015 Update 3 RTM?