Fixing the CI failure by fixing the infinite loop in Commerce

[amatsuda]

It seems that current faker master is broken https://travis-ci.org/github/faker-ruby/faker/builds since 7034961.
What's happening here is that the ko locale data provides only one commerce.department entry where some tests e.g.

faker/test/faker/default/test_faker_commerce.rb

Line 31 in d9b9ad9

assert_match ' & ', @tester.department(max: 2, fixed_amount: true)

expects more than two commerce.department entries to exist, and because this loop never ends until it successfully fetches the given number of categories, it results in an infinite loop.

This is rather a code bug than a data inadequacy. No code should cause such an infinite loop regardless of given data.

This patch firstly extends the existing sample method to take an argument in the same manner as Ruby's Array#sample.
Then now we can simplify the code by using this new sample with number instead of fetching multiple times inside the loop.