Update rand dependencies to those in 0.7

[jonhoo]

I'm not sure if this still satisfies the minimum supported Rust version guarantees of criterion, but figured I'd put a PR up regardless that can be merged when appropriate :)

[bheisler]

Hey, thanks for the pull request.

Normally, my policy is to not accept pull requests that only update dependencies. However, in this case it looks like you've updated some code as well, to handle compatibility concerns with the newer version. That saves me the trouble of figuring that out myself. I'll probably merge this into the 0.3.0 development branch later, after checking for compatibility with rustc.

[jonhoo]

Yeah, the changes are pretty minor, but always annoying to have to chase them down yourself.

As for CI, https://travis-ci.org/bheisler/criterion.rs/jobs/563113700 (macOS) seems to be a spurious failure, whereas the 1.26.0 tests fail with:

error: no matching package named `getrandom_package` found

My guess is that this is related to the move to the 2018 edition so that older versions of the compiler are no longer supported by the new version of rand.

[ignatenkobrain]

my policy is to not accept pull requests that only update dependencies

Why not? This saves people quite some time… Especially package maintainers in distros.

[bheisler]

Why not? This saves people quite some time… Especially package maintainers in distros.

I update all of the dependencies myself just before publishing a new version. I'm not sure why distro package maintainers would care what happens in the repo between published versions?

[bheisler]

Merged into v0.3.0-dev. Thanks!