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. Since the update, if you only hash 20 characters, you end up getting 'DENIED' back for the session ID.
Update tests for hash substring change
Merge pull request #2 from EvanDotPro/patch-1

Change hash substring to be 26 characters instead of 20.