Update minimal supported Ruby version in the ruby-fizzbuzz.gemspec file
Update minimal supported Ruby version in the ruby-fizzbuzz.gemspec file

Signed-off-by: Krzysztof Wilczyński <5f1c0be89013f8fde969a8dcb2fa1d522e94ee00@linux.com>

kwilczynski/ruby-fizzbuzz,kwilczynski/ruby-fizzbuzz,kwilczynski/ruby-fizzbuzz