dialect/sql/sqlgraph: add update node api

Summary: Pull Request resolved: https://github.com/facebookincubator/ent/pull/222

Reviewed By: alexsn

Differential Revision: D18833733

fbshipit-source-id: e833d84f4e5e5c73b1c85e7387472c9a87b7947e

entc/integration/integration_test.go

@@ -195,6 +195,7 @@ func Sanity(t *testing.T, client *ent.Client) {
 	usr = client.User.UpdateOne(usr).SetName("baz").AddGroups(grp).SaveX(ctx)
 	require.Equal("baz", usr.Name)
 	require.NotEmpty(usr.QueryGroups().AllX(ctx))
+
 	// grouping.
 	var v []struct {
 		Name  string `json:"name"`