Stack v1.5.1 Release Candidate

[Emanuel Borsboom]

I've built the stack-1.5.1 binaries (except for ARM, which takes a bit longer).  Give them a try if you wish; you can get them here: https://github.com/commercialhaskell/stack/releases/tag/v1.5.1-rc1

Assuming I hear no reports of trouble, I'll be releasing these in the next day or two (whenever the ARM binary finishes building).