Bug when variant value has `as <type>`

[faern]

Really handy crate 👌

But I have found that if used on an enum like this:

#[derive(TryFromPrimitive)]
#[repr(u8)]
pub enum Bar {
    A = 10,
    B = 20 as u8,
}

it produces the following code:

impl Bar {
    pub fn try_from(n: u8) -> Option<Bar> {
        match n {
            10u8 => Some(Bar::A),
            10u8 => Some(Bar::B),
            _ => None,
        }
    }
}

Which is clearly wrong, because now Bar::try_from(20) will return None instead of Some(Bar::B).