cargo: bump once_cell from 1.7.2 to 1.8.0

Bumps [once_cell](https://github.com/matklad/once_cell) from 1.7.2 to 1.8.0.
- [Release notes](https://github.com/matklad/once_cell/releases)
- [Changelog](https://github.com/matklad/once_cell/blob/master/CHANGELOG.md)
- [Commits](https://github.com/matklad/once_cell/compare/v1.7.2...v1.8.0)

---
updated-dependencies:
- dependency-name: once_cell
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Cargo.lock

@@ -2449,9 +2449,9 @@ checksum = "1a5b3dd1c072ee7963717671d1ca129f1048fda25edea6b752bfc71ac8854170"
 
 [[package]]
 name = "once_cell"
-version = "1.7.2"
+version = "1.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "af8b08b04175473088b46763e51ee54da5f9a164bc162f615b91bc179dbf15a3"
+checksum = "692fcb63b64b1758029e0a96ee63e049ce8c5948587f2f7208df04625e5f6b56"
 
 [[package]]
 name = "oorandom"

Cargo.toml

@@ -47,7 +47,7 @@ native-tls = "0.2.3"
 num_cpus = "1.13.0"
 num-derive = "0.3.0"
 num-traits = "0.2.6"
-once_cell = "1.4.1"
+once_cell = "1.8.0"
 percent-encoding = "2.0"
 pgp = { version = "0.7.0", default-features = false }
 pretty_env_logger = { version = "0.4.0", optional = true }