Fix deprecation in specs

Created by: zzet

DEPRECATION: expect { }.not_to raise_error(SpecificErrorClass) is deprecated. Use expect { }.not_to raise_error (with no args) instead. Called from /home/travis/build/gitlabhq/gitlabhq/spec/tasks/gitlab/backup_rake_spec.rb:42:in `block (4 levels) in <top (required)>'.