Address comments from Daniel, move the schema change to v3.4.

Signed-off-by: Liping Xue <lipingxue@gmail.com>

Author: lipingxue

cli/compose/loader/full-example.yml

@@ -1,4 +1,4 @@
-version: "3.3"
+version: "3.4"
 
 services:
   foo:

cli/compose/loader/loader.go

@@ -445,7 +445,11 @@ func LoadVolumes(source map[string]interface{}) (map[string]types.VolumeConfig,
 				volume.External.Name = name
 				volumes[name] = volume
 			} else {
-				logrus.Warnf("invalid to specify name for external volume: %s", volume.External.Name)
+				logrus.Warnf("volume %s: volume.external.name is deprecated, please use volume.name", name)
+
+				if volume.Name != "" {
+					return nil, errors.Errorf("volume %s: volume.external.name and volume.name conflict, only use volume.name", name)
+				}
 			}
 		}
 	}