Fixes gemspec to allow building of gem

Your gem push was probably failing because there was no '.gem' file, and there was probably no '.gem' file because the 'gem build fizzbuzz_jac.gemspec' command was failing due the corrections listed in this commit. Here's how it might be remedied:

1. Fix the gemspec file like in the PR.
2. Run the build command: 'gem build fizzbuzz_jac.gemspec'
3. Then try your 'gem push' command.

I hope you can find this helpful :)