Update approx to 0.5

Author: djc

Cargo.toml

@@ -20,7 +20,7 @@ byteorder = "1"
 fnv = "1"
 itertools = "0.11"
 murmur3 = "0.5"
-ndarray = "0.15"
+ndarray = { version = "0.15", features = ["approx-0_5"] }
 ordered-float = "4"
 rand = "0.8"
 rand_chacha = "0.3"
@@ -39,7 +39,7 @@ default = ["memmap"]
 memmap = ["memmap2"]
 
 [dev-dependencies]
-approx = "0.4"
+approx = "0.5"
 criterion = "0.3"
 lazy_static = "1"
 maplit = "1"