Use `SecureRandom.hex` instead of `generate_id`

[joker1007]

I have the same probrem with https://github.com/ixixi/fluent-plugin-sqs/pull/35

In the first place, plugin does not need to have implementation for Unique ID generation In this case, plugin can use SecureRandom.

For your information, I benchmarked each performance. SecureRandom is obviously safer and faster.

% ruby unique_id_bench.rb
Warming up --------------------------------------
        securerandom    54.085k i/100ms
         generate_id    11.633k i/100ms
Calculating -------------------------------------
        securerandom    658.520k (± 0.9%) i/s -      3.299M in   5.010460s
         generate_id    122.832k (± 1.3%) i/s -    616.549k in   5.020287s

Comparison:
        securerandom:   658519.5 i/s
         generate_id:   122831.7 i/s - 5.36x  slower

require 'securerandom'
require 'benchmark/ips'

def generate_id
  unique_val = ((('a'..'z').to_a + (0..9).to_a)*3).shuffle[0,(rand(10).to_i)].join
  Time.now.to_i.to_s + unique_val
end

Benchmark.ips do |x|
  x.report("securerandom") { SecureRandom.hex(16) }
  x.report("generate_id") { generate_id }

  x.compare!
end

[erickhun]

appreciate the fix @ixixi