Update rand_chacha requirement from ~0.2.2 to ~0.3.1

[dependabot[bot]]

Updates the requirements on rand_chacha to permit the latest version.

Changelog

Sourced from rand_chacha's changelog.

[0.3.19] - 2017-12-27

Changed

• Require log <= 0.3.8 for dev builds
• Update fuchsia-zircon dependency to 0.3
• Fix broken links in docs (to unblock compiler docs testing CI)

[0.3.18] - 2017-11-06

Changed

• thread_rng is seeded from the system time if OsRng fails
• weak_rng now uses thread_rng internally

[0.3.17] - 2017-10-07

Changed

• Fuchsia: Magenta was renamed Zircon

[0.3.16] - 2017-07-27

Added

• Implement Debug for mote non-public types
• implement Rand for (i|u)i128
• Support for Fuchsia

Changed

• Add inline attribute to SampleRange::construct_range. This improves the benchmark for sample in 11% and for shuffle in 16%.
• Use RtlGenRandom instead of CryptGenRandom

[0.3.15] - 2016-11-26

Added

• Add Rng trait method choose_mut
• Redox support

Changed

• Use arc4rand for OsRng on FreeBSD.
• Use arc4random(3) for OsRng on OpenBSD.

Fixed

• Fix filling buffers 4 GiB or larger with OsRng::fill_bytes on Windows

[0.3.14] - 2016-02-13

Fixed

• Inline definitions from winapi/advapi32, which decreases build times

[0.3.13] - 2016-01-09

Fixed

• Compatible with Rust 1.7.0-nightly (needed some extra type annotations)

... (truncated)

Commits

• 98a0339 Merge pull request #1135 from dhardy/work
• a7f8fb7 Prepare rand_chacha v0.3.1 release
• 09d3df3 Merge pull request #1130 from dhardy/work
• d167dd2 Deprecate ReadRng
• e3bc4a1 Do not impl serde for ReadRng or ReseedingRng
• 66b1636 Merge pull request #1132 from rust-random/readme-wasm-note
• d9c6a76 README: add note regarding wasm32-unknown-unknown
• 4726d32 Update minimum version of packed_simd_2
• f6bbfcf serde for BlockRng, ReseedingRng and ReadRng
• 2732f2d Merge pull request #1116 from vks/criterion
• Additional commits viewable in compare view

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