Change hash substring to be 26 characters instead of 20.

Cleverbot released an update that requires the first 26 characters after `stimulus=` in the post body to be hashed for the `incognocheck` parameter. Previously it only required the first 20, however if you only hash 20 characters, you end up getting 'DENIED' back for the session ID.

This solves issue #2.
Merge pull request #3 from EvanDotPro/patch-1

Change hash substring to be 26 characters instead of 20.