Fix project models specs

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

spec/models/project_spec.rb

@@ -70,7 +70,7 @@
 
     it "should not allow new projects beyond user limits" do
       project2 = build(:project)
-      project2.stub(:creator).and_return(double(can_create_project?: false, projects_limit: 0))
+      project2.stub(:creator).and_return(double(can_create_project?: false, projects_limit: 0).as_null_object)
       project2.should_not be_valid
       project2.errors[:limit_reached].first.should match(/Your own projects limit is 0/)
     end