Unable to use hex literals in call

[HCastano]

I have an ink! method with the following signature:

type Foo {
    selector: [u8; 4],
}

fn bar(&mut self, f: Foo)

When using cargo-contract to supply the argument I have to use the decimal
representation for the bytes:

cargo contract call \
     --contract ... \
     --message bar \
     --args "Foo { selector: [123, 456, 789, 987] }" \
     --suri ... \

I'd like the option to use hex literals as well:

cargo contract call \
     --contract ... \
     --message bar \
     --args "Foo { selector: [0xAB, 0xCD, 0xEF, 0xGH] }" \
     --suri ... \

This is how ink! mainly deals with selectors, so it would make it more consistent for
users.