Fix / suppress JitterRng x86_64-apple-darwin test? #55
Description
This CI run failed due to CoarseTimer: https://travis-ci.org/dhardy/rand/jobs/303686167
---- gen_u64_jitter stdout ----
thread 'gen_u64_jitter' panicked at 'called `Result::unwrap()` on an `Err` value: Error { kind: Unavailable, msg: "timer jitter failed basic quality tests", cause: Some(CoarseTimer) }', src/libcore/result.rs:906:4
note: Run with `RUST_BACKTRACE=1` for a backtrace.
---- init_jitter stdout ----
thread 'init_jitter' panicked at 'called `Result::unwrap()` on an `Err` value: Error { kind: Unavailable, msg: "timer jitter failed basic quality tests", cause: Some(CoarseTimer) }', src/libcore/result.rs:906:4
I'm a bit surprised that it failed on a common platform. Note that this test is part of the benchmark, which is only run in nightly builds, of which we only have two. Should we add regular tests? Should we simply not test JitterRng because we can't expect it to run on all platforms?