Redmine

Hi there!

I have installed the plugin on my new Redmine 3.0, configured it, but when I try to manage the comitters of the repository I just added to my project I get this error:

```
Started GET "/repositories/3/committers" for xxx at 2015-03-08 20:40:37 +0100
Processing by RepositoriesController#committers as HTML
Parameters: {"id"=>"3"}
Current user: leobaillard (id=3)
Completed 500 Internal Server Error in 24ms

NoMethodError (undefined method `compact!' for #<User::ActiveRecord_Relation:0xb27a3e1c>):
app/controllers/repositories_controller.rb:98:in `committers'
```

Here the patch :

Before :

  def committers
    @committers = @repository.committers
    @users = @project.users
    additional_user_ids = @committers.collect(&:last).collect(&:to_i) - @users.collect(&:id)

After :

  def committers
    @committers = @repository.committers
    @users = @project.users.collect(&:id)
    additional_user_ids = @committers.collect(&:last).collect(&:to_i) - @users

Thank you!