Replace path to cargo registry with normalized path

[bkchr]

This is required as the path is different for every user.

Old behavior:

   ::: /usr/local/cargo/registry/src/github.com-1ecc6299db9ec823/parity-scale-codec-2.2.0/src/codec.rs:284:18
    |
284 |     fn decode<I: Input>(input: &mut I) -> Result<Self, Error>;
    |                  ----- required by this bound in `pallet::_::_parity_scale_codec::Decode::decode`

New behavior:

   ::: $CARGO_REGISTRY/github.com-1ecc6299db9ec823/parity-scale-codec-2.2.0/src/codec.rs
    |
    |     fn decode<I: Input>(input: &mut I) -> Result<Self, Error>;
    |                  ----- required by this bound in `pallet::_::_parity_scale_codec::Decode::decode`

[bkchr]

CC @dtolnay

[dtolnay]

Thanks!