chore(deps): bump prometheus from 0.11.0 to 0.12.0 (#116)

Bumps [prometheus](https://github.com/tikv/rust-prometheus) from 0.11.0 to 0.12.0.
- [Release notes](https://github.com/tikv/rust-prometheus/releases)
- [Changelog](https://github.com/tikv/rust-prometheus/blob/master/CHANGELOG.md)
- [Commits](tikv/rust-prometheus@v0.11.0...v0.12.0)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Cargo.lock

@@ -16,7 +16,7 @@ path = "src/main.rs"
 [dependencies]
 hyper = { version = "0.14", features = ["stream", "http1", "http2", "server", "runtime"] }
 lazy_static = "1.4"
-prometheus = "0.11"
+prometheus = "0.12"
 tracing = "0.1"
 tracing-subscriber = { version = "0.2", features = ["parking_lot"] }
 tracing-futures = { version = "0.2", features = ["futures-03"] }