Sets date for 2.9.1 release

Author: weierophinney

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 All notable changes to this project will be documented in this file, in reverse chronological order by release.
 
-## 2.9.1 - TBD
+## 2.9.1 - 2018-12-17
 
 ### Added
 
@@ -22,8 +22,8 @@ All notable changes to this project will be documented in this file, in reverse
 
 ### Fixed
 
-- [#79](https://github.com/zendframework/zend-filter/pull/79) Fix regression bug introduced in 2.9.0 when using
-  `Zend\Filter\File\RenameUpload` via the traditional SAPI
+- [#79](https://github.com/zendframework/zend-filter/pull/79) fixes a regression introduced in 2.9.0 when using
+  `Zend\Filter\File\RenameUpload` via the traditional SAPI.
 
 ## 2.9.0 - 2018-12-12