mozilla_reduceright.rb - fix regex error.

[] is character class, and will match on 1, 6, 7, and |.
Where as (16|17) will match on either 16, or 17.

irb(main):053:0> y = /Firefox\/3\.6\.[16|17]/
=> /Firefox\/3\.6\.[16|17]/
irb(main):054:0> x = "Firefox/3.6.13"
=> "Firefox/3.6.13"
irb(main):055:0> x =~ y
=> 0
irb(main):056:0> y = /Firefox\/3\.6\.(16|17)/
=> /Firefox\/3\.6\.(16|17)/
irb(main):057:0> x =~ y
=> nil
Land #1956 - fix regex error for mozilla_reduceright.rb