service: Use OrderedDict to preserve volumes order on versions prior 3.6.

Signed-off-by: Antony MECHIN <[email protected]>

compose/service.py

@@ -1429,7 +1429,7 @@ def merge_volume_bindings(volumes, tmpfs, previous_container, mounts):
     """
     affinity = {}
 
-    volume_bindings = dict(
+    volume_bindings = OrderedDict(
         build_volume_binding(volume)
         for volume in volumes
         if volume.external