Apply OrderedDict changes to Bundle.

stix2/bundle.py

@@ -1,5 +1,7 @@
 """STIX 2 Bundle object"""
 
+from collections import OrderedDict
+
 from .base import _STIXBase
 from .properties import IDProperty, Property, TypeProperty
 
@@ -7,12 +9,13 @@ from .properties import IDProperty, Property, TypeProperty
 class Bundle(_STIXBase):
 
     _type = 'bundle'
-    _properties = {
-        'type': TypeProperty(_type),
-        'id': IDProperty(_type),
-        'spec_version': Property(fixed="2.0"),
-        'objects': Property(),
-    }
+    _properties = OrderedDict()
+    _properties = _properties.update([
+        ('type', TypeProperty(_type)),
+        ('id', IDProperty(_type)),
+        ('spec_version', Property(fixed="2.0")),
+        ('objects', Property()),
+    ])
 
     def __init__(self, *args, **kwargs):
         # Add any positional arguments to the 'objects' kwarg.