Adds CHANGELOG entry for #102

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 All notable changes to this project will be documented in this file, in reverse chronological order by release.
 
-## 2.8.4 - TBD
+## 2.8.4 - 2018-01-31
 
 ### Added
 
@@ -34,6 +34,12 @@ All notable changes to this project will be documented in this file, in reverse
   case whereby if the special `__ZF` session value is a non-array value,
   initializing the session would result in errors.
 
+- [#102](https://github.com/zendframework/zend-session/pull/102) fixes an issue
+  introduced with 2.8.0 with `AbstractContainer::offsetGet`. Starting in 2.8.0,
+  if the provided `$key` did not exist, the method would raise an error
+  regarding an invalid variable reference; this release provides a fix that
+  resolves that issue.
+
 ## 2.8.3 - 2017-12-01
 
 ### Added