[TargetIntegrator] Unstub update method when testing it

spec/unit/installer/user_project_integrator/target_integrator_spec.rb

@@ -51,6 +51,7 @@ module Pod
         end
 
         it 'fixes the "Link binary with libraries" build phase of legacy installations' do
+          @target_integrator.unstub(:update_to_cocoapods_0_39)
           @pod_bundle.stubs(:requires_frameworks? => true)
           @target_integrator.integrate!
           target = @target_integrator.send(:native_targets).first