Switch to SHA384_Final()
Switch to SHA384_Final()

This was working previously because the Openssl libcrypto implementation
calls SHA512_Final directly from SHA384_Final. What if this changes?

I don't think the increase in confusion here justifies the decrease
in stack depth.

fixes #157

bpdavidson/s2n,gibson-compsci/s2n,awslabs/s2n,alexeblee/s2n,raycoll/s2n,gibson-compsci/s2n,raycoll/s2n,colmmacc/s2n,wcs1only/s2n,gibson-compsci/s2n,colmmacc/s2n,awslabs/s2n,wcs1only/s2n,PKRoma/s2n,PKRoma/s2n,colmmacc/s2n,alexeblee/s2n,bpdavidson/s2n,awslabs/s2n,awslabs/s2n,jldodds/s2n,bpdavidson/s2n,awslabs/s2n,colmmacc/s2n,bpdavidson/s2n,gibson-compsci/s2n,awslabs/s2n,jldodds/s2n,bpdavidson/s2n,raycoll/s2n,raycoll/s2n,gibson-compsci/s2n,PKRoma/s2n,PKRoma/s2n,PKRoma/s2n,jldodds/s2n,alexeblee/s2n,jldodds/s2n,alexeblee/s2n,wcs1only/s2n,bpdavidson/s2n,colmmacc/s2n,alexeblee/s2n,raycoll/s2n,PKRoma/s2n,wcs1only/s2n,jldodds/s2n,PKRoma/s2n,wcs1only/s2n,raycoll/s2n,wcs1only/s2n,wcs1only/s2n,alexeblee/s2n,PKRoma/s2n,gibson-compsci/s2n,wcs1only/s2n,colmmacc/s2n