modify tests for python 3.x acceptance

stix2/test/test_datastore.py

@@ -215,7 +215,8 @@ def test_filter_value_type_check():
     with pytest.raises(TypeError) as excinfo:
         Filter('created', '=', object())
     # On Python 2, the type of object() is `<type 'object'>` On Python 3, it's `<class 'object'>`.
-    assert "Filter value of '<type 'object'>' is not supported" in str(excinfo.value)
+    assert any([s in str(excinfo.value) for s in ["<type 'object'>", "'<class 'object'>'"]])
+    assert "is not supported. The type must be a Python immutable type or dictionary" in str(excinfo.value)
 
     with pytest.raises(TypeError) as excinfo:
         Filter("type", "=", complex(2, -1))