Fix: Corrected Display unit mismatch.

[morugetsm]

Updated the documentation to match the actual code behavior.

use bytesize::ByteSize;

fn main() {
    let foo = ByteSize(12345678);

    println!("Default   {}", foo);
    println!("iec       {}", foo.display().iec());
    println!("iec_short {}", foo.display().iec_short());
    println!("si        {}", foo.display().si());
    println!("si_short  {}", foo.display().si_short());
}

Default   11.8 MiB
iec       11.8 MiB
iec_short 11.8M
si        12.3 MB
si_short  12.3M

I arbitrarily changed the numbers to make the difference more noticeable, but feel free to adjust them if there are better values to express it.

[robjtede]

nice one, thank you 👍🏻