Update release notes for 4.0.0b3 (#659)

Author: garrettheel

docs/release_notes.rst

@@ -1,7 +1,7 @@
 Release Notes
 =============
 
-v4.0.0b2
+v4.0.0b3
 --------
 
 :date: 2019-04-10
@@ -40,6 +40,10 @@ When upgrading, pay special attention to use of ``**filters`` and ``**expected_v
 attribute names. Also keep an eye out for kwargs like ``user_id__eq=5`` or ``email__null=True``, which are no longer supported. If you're not already using
 ``mypy`` to type check your code, it can help you catch cases like these.
 
+New features in this release:
+
+* Support for Transactions (``TransactGet`` and ``TransactWrite``) (#618)
+
 Other changes in this release:
 
 * Python 2.6 is no longer supported. 4.x.x will be the last major release to support Python 2.7 given the upcoming EOL.

pynamodb/__init__.py

@@ -7,4 +7,4 @@
 """
 __author__ = 'Jharrod LaFon'
 __license__ = 'MIT'
-__version__ = '4.0.0b2'
+__version__ = '4.0.0b3'