Try the following command:

    printf "\x1f\x8b\x08\x00\x00\x00\x00\x00" | cat - .git/objects/c0/fb67ab3fda7909000da003f4b2ce50a53f43e7 | gunzip

No external tools are needed.

<sup>Source: [How to uncompress zlib data in UNIX?][1] at unix SE</sup>


  [1]: https://unix.stackexchange.com/questions/22834/how-to-uncompress-zlib-data-in-unix