Update HISTORY.rst

Author: PJSimon

HISTORY.rst

@@ -11,6 +11,10 @@ Next release
 - Sensitive language replacement (`#609 <https://github.com/box/box-python-sdk/pull/609>`_)
 - Add BoxSign support (`#617 <https://github.com/box/box-python-sdk/pull/617>`_)
 
+**Bug Fixes:**
+
+- Upgrade cryptography to version 3 (`#620 <https://github.com/box/box-python-sdk/pull/620>`_)
+
 2.12.1 (2021-06-16)
 ++++++++