[openrr-gui] Pin zerocopy to 0.3.0

[taiki-e]

zerocopy 0.3.1 removed support for stable Rust. We want to use stable, so pin zerocopy to 0.3.0.

details

zerocopy 0.3.1 depends on min_const_generics that requires 1.51.0 (the current beta, it will be released as stable in 2021-03-25).
Therefore, it cannot be used in the current stable (1.50.0).

https://github.com/openrr/openrr/runs/2036728847?check_suite_focus=true

error[E0658]: const generics are unstable
   --> /home/runner/.cargo/registry/src/6github.com-1ecc6299db9ec823/zerocopy-0.3.1/src/lib.rs:71:38
    |
71  |         unsafe impl<T: $trait, const N: usize> $trait for [T; N] {
    |                                      ^
...
263 | impl_for_composite_types!(FromBytes);
    | ------------------------------------- in this macro invocation
    |
    = note: see issue #74878 <https://github.com/rust-lang/rust/issues/74878> for more information
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

cc @joshlf Is this intentional? If so, it would be nice to have a note that warns us about stable Rust support is not guaranteed.

[joshlf]

This was a mistake - I've yanked 0.3.1, and will be releasing these changes as 0.4.0. Thanks for bringing this to my attention, and sorry for the breakage!

[taiki-e]

@joshlf Thanks for the fix!

[joshlf]

np!