Remove redefinition of `Enumberable#reduce`

The code currently refines [`Enumerable#reduce`](http://ruby-doc.org/core-2.0/Enumerable.html#method-i-reduce), which is now standard on ruby 2.0.0. The redefinition is not compatible with the canonical one. Of course, this is causing problems.

For example, running a rails console:

    Loading development environment (Rails 3.2.13)
    2.0.0dev :001 > [].reduce({}, :merge)
     => {} 
    2.0.0dev :002 > require 'UniversalDetector'
     => true 
    2.0.0dev :003 > [].reduce({}, :merge)
     => :merge 


This patch remove the redefinition and change the only usage of this method to be compatible with ruby 2.0.0.

If possible, consider pushing a new version for this fix.