volume: fix missing size in table output (#39)

Author: René Moser

cloudscale_cli/commands/volume.py

@@ -18,6 +18,7 @@ def volume(ctx):
         [].{
             "name": name,
             "type": type,
+            "size_gb": size_gb,
             "tags": tags,
             "server_uuids": server_uuids,
             "zone": zone.slug,