Make test_sprocketize use the interpreter that runs it

Author: snu5mumr1k

test/test_sprocketize.rb

@@ -85,6 +85,6 @@ def teardown
   def sprockets(*args)
     script = File.expand_path("../../bin/sprockets", __FILE__)
     lib    = File.expand_path("../../lib", __FILE__)
-    `ruby -I#{lib} #{script} #{Shellwords.join(args)} 2>&1`
+    `#{RbConfig.ruby} -I#{lib} #{script} #{Shellwords.join(args)} 2>&1`
   end
 end