Update rand requirement from 0.7.3 to 0.8.4

[dependabot-preview]

Updates the requirements on rand to permit the latest version.

Changelog

Sourced from rand's changelog.

[0.8.4] - 2021-06-15

Additions

• Use const-generics to support arrays of all sizes (#1104)
• Implement Clone and Copy for Alphanumeric (#1126)
• Add Distribution::map to derive a distribution using a closure (#1129)
• Add Slice distribution (#1107)
• Add DistString trait with impls for Standard and Alphanumeric (#1133)

Other

• Reorder asserts in Uniform float distributions for easier debugging of non-finite arguments (#1094, #1108)
• Add range overflow check in Uniform float distributions (#1108)
• Deprecate rngs::adapter::ReadRng (#1130)

[0.8.3] - 2021-01-25

Fixes

• Fix no-std + alloc build by gating choose_multiple_weighted on std (#1088)

[0.8.2] - 2021-01-12

Fixes

• Fix panic in UniformInt::sample_single_inclusive and Rng::gen_range when providing a full integer range (eg 0..=MAX) (#1087)

[0.8.1] - 2020-12-31

Other

• Enable all stable features in the playground (#1081)

[0.8.0] - 2020-12-18

Platform support

• The minimum supported Rust version is now 1.36 (#1011)
• getrandom updated to v0.2 (#1041)
• Remove wasm-bindgen and stdweb feature flags. For details of WASM support, see the getrandom documentation. (#948)
• ReadRng::next_u32 and next_u64 now use little-Endian conversion instead of native-Endian, affecting results on Big-Endian platforms (#1061)
• The nightly feature no longer implies the simd_support feature (#1048)
• Fix simd_support feature to work on current nightlies (#1056)

Rngs

• ThreadRng is no longer Copy to enable safe usage within thread-local destructors (#1035)
• gen_range(a, b) was replaced with gen_range(a..b). gen_range(a..=b) is also supported. Note that a and b can no longer be references or SIMD types. (#744, #1003)
• Replace AsByteSliceMut with Fill and add support for [bool], [char], [f32], [f64] (#940)
• Restrict rand::rngs::adapter to std (#1027; see also #928)
• StdRng: add new std_rng feature flag (enabled by default, but might need to be used if disabling default crate features) (#948)
• StdRng: Switch from ChaCha20 to ChaCha12 for better performance (#1028)
• SmallRng: Replace PCG algorithm with xoshiro{128,256}++ (#1038)

Sequences

... (truncated)

Commits

• 8792268 Merge pull request #1137 from rust-random/work2
• 1bfc53d Update changelogs and bump version numbers
• 4534311 Merge pull request #1133 from rust-random/work2
• 81f1af8 Correct usage of reserve
• fa17d1c Add comment to append_string for Standard
• b4c1d66 Add DistString
• 1947c89 Move Distribution trait and associates to sub-module
• 98a0339 Merge pull request #1135 from dhardy/work
• a7f8fb7 Prepare rand_chacha v0.3.1 release
• 09d3df3 Merge pull request #1130 from dhardy/work
• Additional commits viewable in compare view

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