Increase version to 3.9.1

docs/main/changelog.rst

@@ -7,6 +7,12 @@ that were made in every particular version.
 From version 0.7.6 *Dependency Injector* framework strictly 
 follows `Semantic versioning`_
 
+3.9.1
+-----
+- Fix docs build problem (``sphinx`` is frozen on ``1.5.6`` version because of
+  incompatibility with ``sphinxcontrib-discus``). 
+- Add badge for docs.
+
 3.9.0
 -----
 - Change initialization of declarative container, so it accepts overriding 

src/dependency_injector/__init__.py

@@ -1,6 +1,6 @@
 """Dependency injector top-level package."""
 
-__version__ = '3.9.0'
+__version__ = '3.9.1'
 """Version number that follows semantic versioning.
 
 :type: str