Update CHANGELOG.rst

Author: wangzlei

CHANGELOG.rst

@@ -2,8 +2,12 @@
 CHANGELOG
 =========
 
+Unreleased
+==========
+
 2.10.0
 ==========
+* bugfix: Only import future for py2. `PR343 <https://github.com/aws/aws-xray-sdk-python/pull/343>`_.
 * bugfix: Defensively copy context entities to async thread. `PR340 <https://github.com/aws/aws-xray-sdk-python/pull/340>`_.
 * improvement: Added support for IGNORE_ERROR option when context is missing. `PR338 <https://github.com/aws/aws-xray-sdk-python/pull/338>`_.