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...0.16.0)

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

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

Cargo.toml

@@ -105,7 +105,7 @@ jemallocator = { version = "0.5", optional = true }
 roots = "0.0.8"
 
 # Least squares solver
-ndarray = { version = "0.15", features = ["approx"] }
+ndarray = { version = "0.16", features = ["approx"] }
 modcholesky = "0.1"