Update version to 3.8.0

Author: rmk135

docs/main/changelog.rst

@@ -7,6 +7,13 @@ that were made in every particular version.
 From version 0.7.6 *Dependency Injector* framework strictly 
 follows `Semantic versioning`_
 
+3.8.0
+-----
+- Add ``DeclarativeContainer.containers`` attribute that stores dictionary of
+  nested containers.
+- Fix bug related to double-overridden providers (provider1 -> provider2 ->
+  provider3).
+
 3.7.1
 -----
 - Add support of six 1.11.0.

src/dependency_injector/__init__.py

@@ -1,6 +1,6 @@
 """Dependency injector top-level package."""
 
-__version__ = '3.7.1'
+__version__ = '3.8.0'
 """Version number that follows semantic versioning.
 
 :type: str