Failed to build fuzzymatch-rs with stable rust

[rabbitinspace]

Environment (please complete the following information):

• OS: Arch 5.4.2-arch1-1
• NeoVim version: v0.4.3
• vim-clap version: master e93e4f1
• Have you reproduced with a minimal vimrc: Yes

Describe the bug
Right now run-cargo task trying to build fuzzymatch-rs crate using stable rust but fails due to pyo3 requires nightly compiler: PyO3/pyo3#5. As a result call to clap#helper#build_all does not build the extension.

To Reproduce
Easiest way is to cd into pythonx/clap and run make build.

Or:

1. Create the minimal vimrc min.vim:

set nocompatible
syntax on
filetype plugin indent on

call plug#begin(stdpath('data') . '/plugged') 
Plug 'liuchengxu/vim-clap', { 'do': function('clap#helper#build_all') }
call plug#end() 

2. Start Neovim with command: nvim -u min.vim

3. Type :PlugInstall

4. See error

cargo build --release
    Finished release [optimized] target(s) in 0.01s
cd pythonx/clap && make build
make[1]: Entering directory '/home/rbbtnspc/.local/share/nvim/plugged/vim-clap/pythonx/clap'
\033[1;34m==>\033[0m Trying to build rust extension
   Compiling pyo3 v0.8.3
error: failed to run custom build command for `pyo3 v0.8.3`

Caused by:
  process didn't exit successfully: `/home/rbbtnspc/.local/share/nvim/plugged/vim-clap/pythonx/clap/fuzzymatch-rs/target/release/build/pyo3-8022947417df982e/build-script-build` (exit code: 101)
--- stderr
thread 'main' panicked at 'Error: pyo3 requires a nightly or dev version of Rust.', /home/rbbtnspc/.cargo/registry/src/github.jparrowsec.cn-1ecc6299db9ec823/pyo3-0.8.3/build.rs:542:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

make[1]: *** [Makefile:18: run-cargo] Error 101
make[1]: Leaving directory '/home/rbbtnspc/.local/share/nvim/plugged/vim-clap/pythonx/clap'
make: *** [Makefile:7: rust-ext] Error 2

Expected behavior
It's expected that the extension will build successfully

Additional information
Building the crate with cargo +nightly build --release fixes the issue but requires nightly compiler.

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