Use GNU format tarballs to support longer paths

This fixes errors related to paths being too long, which is common when
using git dependencies. Note that cargo itself switched from UStar to
GNU format in 2020 or so: rust-lang/cargo#8453.

    thread 'main' panicked at src/main.rs:290:32:
        called `Result::unwrap()` on an `Err` value: Custom { kind: Other, error: "provided value is too long when setting path for some-crate-0.123.123/src/" }

Author: cormac-ainc

src/main.rs

@@ -282,7 +282,7 @@ fn build_ar(ar: &mut Builder<GzEncoder<File>>, pkg: &Package, config: &GlobalCon
             relative
         );
 
-        let mut header = Header::new_ustar();
+        let mut header = Header::new_gnu();
         let metadata = file.metadata().unwrap();
         header.set_path(&path).unwrap();
         header.set_metadata(&metadata);