capthca form with 'numeric' code type, returns alphabetical letters on referesh

[memlucky71]

hi
in my form I have:

<%= show_simple_captcha :label => "..." , :code_type => 'numeric' %>

when I open the page in browser I have numerical values in image, but when I click refresh button, alphabetical letters will be replaced in image. I want letters to be numbers, just like refreshing whole page in browser.

[zealot128]

I never used the code_type option by myself, so I didn't notice that behavior after the refresh button was introduced in #3.
I guess, the code type must be given to the refresh link and parsed in the rack middleware.

If you have some time, I would appreciate a pull request :)