join: fix workaround for IntErrorKind

In Rust versions before 1.55, there was no enum for parse errors. With the bump of the MSRV to 1.56 we can simplify this.

src/uu/join/src/join.rs

@@ -18,6 +18,7 @@ use std::error::Error;
 use std::fmt::Display;
 use std::fs::File;
 use std::io::{stdin, stdout, BufRead, BufReader, BufWriter, Split, Stdin, Write};
+use std::num::IntErrorKind;
 #[cfg(unix)]
 use std::os::unix::ffi::OsStrExt;
 use uucore::display::Quotable;
@@ -965,13 +966,9 @@ fn get_field_number(keys: Option<usize>, key: Option<usize>) -> UResult<usize> {
 /// Parse the specified field string as a natural number and return
 /// the zero-based field number.
 fn parse_field_number(value: &str) -> UResult<usize> {
-    // TODO: use ParseIntError.kind() once MSRV >= 1.55
-    // For now, store an overflow Err from parsing a value 10x 64 bit usize::MAX
-    // Adapted from https://github.com/rust-lang/rust/issues/22639
-    let overflow = "184467440737095516150".parse::<usize>().err().unwrap();
     match value.parse::<usize>() {
         Ok(result) if result > 0 => Ok(result - 1),
-        Err(ref e) if *e == overflow => Ok(usize::MAX),
+        Err(e) if e.kind() == &IntErrorKind::PosOverflow => Ok(usize::MAX),
         _ => Err(USimpleError::new(
             1,
             format!("invalid field number: {}", value.quote()),