expr: fix ~ restrict onig version to v4.3.2 (or later patches)

.# Discussion

onig v4.3.0/v4.3.1 inadvertently introduced a new minimum rust version (requiring v1.31+;
see rust-onig/rust-onig#97). This was repaired with v4.3.2, and
onig now specifies that rust minimum version will stay the same for patches, but may
change between minor version increments.

src/expr/Cargo.toml

@@ -10,7 +10,7 @@ path = "expr.rs"
 
 [dependencies]
 libc = "0.2.42"
-onig = "4.2.1"
+onig = "~4.3.2"
 uucore = { path="../uucore" }
 
 [[bin]]