shellexpand fails to build on latest rust nightly

 Compiling shellexpand v3.1.1
   error[E0308]: mismatched types
      --> /home/amir/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/shellexpand-3.1.1/src/funcs.rs:395:21
       |
   394 |                 let var_name = match var_name.as_str() {
       |                                      ----------------- this expression has type `&str`
   395 |                     Some(var_name) => var_name,
       |                     ^^^^^^^^^^^^^^ expected `str`, found `Option<_>`
       |
       = note: expected type `str`
                  found enum `Option<_>`

   error[E0308]: mismatched types
      --> /home/amir/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/shellexpand-3.1.1/src/funcs.rs:397:21
       |
   394 |                 let var_name = match var_name.as_str() {
       |                                      ----------------- this expression has type `&str`
   ...
   397 |                     None => return Ok(None),
       |                     ^^^^ expected `str`, found `Option<_>`
       |
       = note: expected type `str`
                  found enum `Option<_>`