fix clb_listener import error (#805)

Author: hellertang

tencentcloud/resource_tc_clb_listener.go

@@ -351,6 +351,7 @@ func resourceTencentCloudClbListener() *schema.Resource {
 			"target_type": {
 				Type:         schema.TypeString,
 				Optional:     true,
+				Computed:     true,
 				ValidateFunc: validateAllowedStringValue([]string{CLB_TARGET_TYPE_NODE, CLB_TARGET_TYPE_TARGETGROUP}),
 				Description:  "Backend target type. Valid values: `NODE`, `TARGETGROUP`. `NODE` means to bind ordinary nodes, `TARGETGROUP` means to bind target group. NOTES: TCP/UDP/TCP_SSL listener must configuration, HTTP/HTTPS listener needs to be configured in tencentcloud_clb_listener_rule.",
 			},