Update ndarray requirement from 0.15 to 0.16

Updates the requirements on [ndarray](https://github.com/rust-ndarray/ndarray) to permit the latest version.
- [Release notes](https://github.com/rust-ndarray/ndarray/releases)
- [Changelog](https://github.com/rust-ndarray/ndarray/blob/master/RELEASES.md)
- [Commits](rust-ndarray/ndarray@ndarray-rand-0.15.0...0.16.1)

---
updated-dependencies:
- dependency-name: ndarray
  dependency-type: direct:production
...

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

metrics-util/Cargo.toml

@@ -67,7 +67,7 @@ rand_distr = "0.4"
 getopts = "0.2"
 hdrhistogram = { version = "7.2", default-features = false }
 sketches-ddsketch = "0.3"
-ndarray = "0.15"
+ndarray = "0.16"
 ndarray-stats = "0.5"
 noisy_float = "0.2"
 ordered-float = "4.2"