Redmine

Hi there, i'm quite new to this and well i've read the tutorial of how to update and i'm currently stuck, when i run
root@vps-1079881-6817 [/var/www/redmine-2.3.0]# rake generate_secret_token

I am getting this :

Bundler could not find compatible versions for gem "mocha":
In Gemfile:
shoulda (~> 3.3.2) ruby depends on
mocha (= 0.10.5) ruby

mocha (0.13.3)

Should i downgrade mocha or what?. I hope someone can help me :(

Regards