<issue_start><issue_comment>Title: bring makefile rust versions inline with nix
username_0: ## PR summary

@ddd-mtl FYI - this bumps makefile rust version to `nightly-2019-07-14` bringing it inline with nix here - https://github.com/holochain/lib3h/pull/193

## Review checklist 
- [ ] The story has unit or integration tests
- [ ] No new bugs, and any tech-debt is identified and justified
- [ ] There is enough API documentation (how to use)
- [ ] There is enough code documentation (how the code works)
<issue_comment>username_0: In this particular case it was failing because the appveyor.yml wasn't in this branch yet. Also, we seem to be getting stuck behind holochain-rust builds in the queue... I think we should not mark it required for merge until we see how stable it is && if we can get a separate queue for builds