Add `gnu-tar` as a dev dependency

[epk]

Running make all would fail with a fpm error:

bundle exec fpm \
        -t deb \
        -s dir \
        --name="ejson" \
        --version="1.2.1" \
        --package="pkg/ejson_1.2.1_amd64.deb" \
        --license=MIT \
        --category=admin \
        --no-depends \
        --no-auto-depends \
        --architecture=amd64 \
        --maintainer="Shopify <admins@shopify.com>" \
        --description="utility for managing a collection of secrets in source control. Secrets are encrypted using public key, elliptic curve cryptography." \
        --url="https://github.com/Shopify/ejson" \
        ./build/man/=/usr/share/man/ \
        ./build/bin/linux-amd64=/usr/bin/ejson
Debian packaging tools generally labels all files in /etc as config files, as mandated by policy, so fpm defaults to this behavior for deb packages. You can disable this default behavior with --deb-no-default-config-files flag {:level=>:warn}
Process failed: tar failed (exit code 1). Full command was:["tar", "-C", "/var/folders/l2/5wvtps5n1zjb9_bm_8s9m5q00000gn/T/package-deb-build-17bf473b24dc93ae688b16c24f3a402b1315ee53b91db126016a642b9ef4/control", "-zcf", "/var/folders/l2/5wvtps5n1zjb9_bm_8s9m5q00000gn/T/package-deb-build-17bf473b24dc93ae688b16c24f3a402b1315ee53b91db126016a642b9ef4/control.tar.gz", "--owner=0", "--group=0", "--numeric-owner", "."] {:level=>:error}
make: *** [pkg/ejson_1.2.1_amd64.deb] Error 1

I dug into it a bit and found tar bundled with macOS does not support the flag "--owner=0"