Bump version to 4.31.1

Author: rmk135

docs/main/changelog.rst

@@ -7,8 +7,8 @@ that were made in every particular version.
 From version 0.7.6 *Dependency Injector* framework strictly 
 follows `Semantic versioning`_
 
-Development version
--------------------
+4.31.1
+------
 - Fix ``ThreadSafeSingleton`` synchronization issue.
   See issue: `#433 <https://github.com/ets-labs/python-dependency-injector/issues/433>`_.
   Thanks to `@garlandhu <https://github.com/garlandhu>`_ for reporting the issue.

src/dependency_injector/__init__.py

@@ -1,6 +1,6 @@
 """Top-level package."""
 
-__version__ = '4.31.0'
+__version__ = '4.31.1'
 """Version number.
 
 :type: str