Replace Array#shuffle.first with Array#sample

[sferik]

Similar to #17099, Array#shuffle allocates an extra array. Array#sample indexes into the array without allocating an extra array. This is the reason why Array#sample exists. It is also more than 15X faster.

Benchmark

require 'benchmark/ips'

ARRAY = (1..100).to_a

def slow
  ARRAY.shuffle.first
end

def fast
  ARRAY.sample
end

Benchmark.ips do |x|
  x.report('slow') { slow }
  x.report('fast') { fast }
end

Ruby 2.1.2

slow  324806.7 (±8.1%) i/s - 1620738 in 5.028042s
fast 5069719.9 (±9.5%) i/s - 24872400 in 5.011482s