Make bin/jsduck work as input file to ocra.

With the require-rubygems section the file can be run from any
directory as it will know from where to load the jsduck library
files under Windows.

bin/jsduck

@@ -17,6 +17,7 @@
 # For running when gem not installed
 $:.unshift File.dirname(File.dirname(__FILE__)) + "/lib"
 
+require 'rubygems'
 require 'jsduck/app'
 require 'jsduck/options'