uniq! function returns nil. it returns nil at jruby

Hi, all

There is a missed implementation at jruby 1.7.10 (also 1.7.9)
the uniq! function for an array doesn't work properly. 

please, check this issue. 
https://github.com/jruby/jruby/issues/1434

so, here is a workaround-way to use the library in a jruby environment.

It works fine.