unwrap instead of let _

I really prefer using at least unwrap here. If this never happens,
they're equivalent, but if it does happen, with the old code, you
silently continue, and with the new code, you blow up.

crates/tarball/src/lib.rs

@@ -45,7 +45,7 @@ pub async fn download_and_extract(
     let tar_gz = File::open(&tarball_location).unwrap();
     let tar = GzDecoder::new(tar_gz);
     let mut archive = Archive::new(tar);
-    let _ = archive.unpack(&extract_location);
+    archive.unpack(&extract_location).unwrap();
 
     std::fs::remove_file(&tarball_location)
         .or(Err(TarballError::FileSystem("removing tarball failed".to_owned())))