Target still created if invalid `--seed` argument

[kjk]

# fuzzit create target promql --seed corups.tar.gz2
2019/08/05 17:38:10 Creating target...
2019/08/05 17:38:11 open corups.tar.gz2: no such file or directory

This still created a target on the backend. Should validate the file name first and maybe add code to delete target on the backend if something along the way fails.

[yevgenypats]

This is fixed in master. will do a release soon.

[yevgenypats]

fixed in this released. https://github.com/fuzzitdev/fuzzit/releases/tag/v2.4.0