Exit code 2 on successful hash computation
Hi! Thank you for the tool, it's of very much help to me.
There's a problem with exit code which is rather hard to work around in scripts. Exit code is `EXIT_CODE_WRONG_PARAMETERS` even though it seems everything is correct.
```
$ echo 'a' | sha3sum -a Keccak256 -t
b281f21c3943a85591c665728ec58c11c05c8465a23d653c6e00914bcccad2f5 *-
$ echo $?
2
```
I've installed `sha3sum` via `cargo install sha3sum`.
**Version:**
```
% sha3sum --version
sha3sum 1.0.1
```
issue