some crates requires edition2021

[masaki925]

when i run docker build -t masked-lm-image ., got error:

#29 2.935   Downloaded enum-ordinalize v3.1.11
#29 2.935 error: failed to parse manifest at `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/enum-ordinalize-3.1.11/Cargo.toml`
#29 2.935
#29 2.935 Caused by:
#29 2.935   feature `edition2021` is required
#29 2.935
#29 2.935   this Cargo does not support nightly features, but if you
#29 2.935   switch to nightly channel you can add
#29 2.935   `cargo-features = ["edition2021"]` to enable this feature

this is because some dependent crates requires edition2021, eg:

• https://github.com/magiclen/enum-ordinalize/blob/master/Cargo.toml#L5
• https://github.com/magiclen/educe/blob/master/Cargo.toml#L5