Clean up in TestNegotiateAPIVersionEmpty

Signed-off-by: John Stephens <johnstep@docker.com>

client/client_test.go

@@ -193,7 +193,7 @@ func TestNewEnvClientSetsDefaultVersion(t *testing.T) {
 // TestNegotiateAPIVersionEmpty asserts that client.Client can
 // negotiate a compatible APIVersion when omitted
 func TestNegotiateAPIVersionEmpty(t *testing.T) {
-	defer env.PatchAll(t, map[string]string{"DOCKER_API_VERSION": ""})
+	defer env.PatchAll(t, map[string]string{"DOCKER_API_VERSION": ""})()
 
 	client, err := NewEnvClient()
 	assert.NilError(t, err)