fix typo

Co-authored-by: Daniel Hofstetter <[email protected]>

src/uu/hashsum/src/hashsum.rs

@@ -334,7 +334,7 @@ fn create_algo_from_flags(matches: &ArgMatches) -> (&'static str, Box<dyn Digest
  }
  }
 
- let alg = alg.unwrap_or_else(|| crash!(1, "You must specify hash algorithm!"));
+ let alg = alg.unwrap_or_else(|| crash!(1, "You must specify a hash algorithm!"));
  (name, alg, output_bits)
 }