Ruby 3.1 no longer includes prime in the stdlib

[rdlugosz]

As of Ruby 3.1, the prime gem is no longer distributed as a part of the standard library and must be bundled explicitly.

I believe the fix is straightforward: include prime in the gemspec file. However, this should probably be tested on a couple of different Ruby versions in order to verify the change doesn't cause problems for older Rubies.

In the meantime, users of the distribution gem can add prime to their Gemfile and you'll satisfy the missing dependency. For example:

# https://github.com/SciRuby/statsample
gem "distribution"
gem "prime" # No longer in stdlib as of Ruby 3.1

gem "statsample"
gem "matrix" # No longer in stdlib as of Ruby 3.1

Note: similar issue opened on statsample gem