Allow ndarray versions < 0.18

Previously the version constraint was updated to ndarray <= 0.17 but the
0.17 release was yanked and this excludes 0.17.1 and later point
releases. This updates the dependency specification to < 0.18 which will
allow point releass (and which is closer to what was used before PyO3#516).

Author: maffoo

Cargo.toml

@@ -27,7 +27,7 @@ nalgebra = { version = ">=0.30, <0.35", default-features = false, optional = tru
 num-complex = ">= 0.2, < 0.5"
 num-integer = "0.1"
 num-traits = "0.2"
-ndarray = ">= 0.15, <=0.17"
+ndarray = ">= 0.15, < 0.18"
 pyo3 = { version = "0.27.0", default-features = false, features = ["macros"] }
 rustc-hash = "2.0"