Fix bug with services extractor

Change-Id: Ifaa6b54f7e9b0b01b4ef6370e6d3c9eeb8db0227
diff --git a/openstack/blockstorage/v2/snapshots/requests.go b/openstack/blockstorage/v2/snapshots/requests.go
index 5dca94c..666dfe0 100644
--- a/openstack/blockstorage/v2/snapshots/requests.go
+++ b/openstack/blockstorage/v2/snapshots/requests.go
@@ -11,6 +11,8 @@
 	ToVolumeListQuery() (string, error)
 }
 
+// ListOpts holds options for listing Snapshots. It is passed to the snapshot.List
+// function.
 type ListOpts struct {
 	// admin-only option. Set it to true to see all tenant volumes.
 	AllTenants bool `q:"all_tenants"`