update changelog

CHANGELOG.md

 # Python Buildpack Changelog
 
+## v69 (2015-10-12)
+
+Revert to v66.
+
+## v68 (2015-10-12)
+
+Fixed .heroku/venv error with modern apps.
+
+## v67 (2015-10-12)
+
+Further improved cache compatibility with multi and node.js buildpacks.
 
 ## v66 (2015-10-09)
 
@@ -42,4 +53,3 @@ Default Python is now latest 2.7.10. Updated Pip and Distribute.
 - Default Python version is v2.7.10
 - Setuptools updated to v16.0
 - Pip updated to v7.0.1
-