Speedup length hiding comment generation

I believe this to be a faster option, and ran a simple benchmark to test as such:
```ruby
require 'benchmark'
ALPHABET = ('a'..'z').to_a
N = 1000000
Benchmark.bmbm do |x|
  x.report('concatenation') do
    junk = ''
    N.times { junk << ALPHABET.sample }
  end
 
  x.report('join') do
    junk = ALPHABET.sample(N).join
  end
end

# Rehearsal -------------------------------------------------
# concatenation   0.420000   0.000000   0.420000 (  0.418906)
# join            0.000000   0.000000   0.000000 (  0.000019)
# ---------------------------------------- total: 0.420000sec
#
#                     user     system      total        real
# concatenation   0.410000   0.000000   0.410000 (  0.418474)
# join            0.000000   0.000000   0.000000 (  0.000018)
```