Update changelog with fixes implemented in 1.8.2 release

Author: MarkBaker

CHANGELOG.md

@@ -8,6 +8,13 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 ## [Unreleased]
 
 
+## [1.8.2] - 2019-07-08
+
+### Fixed
+
+- Uncaught error when opening ods file and properties aren't defined - [Issue #1047](https://github.com/PHPOffice/PhpSpreadsheet/issues/1047)
+- Xlsx Reader Cell datavalidations bug - [PR #1052](https://github.com/PHPOffice/PhpSpreadsheet/pull/1052)
+
 ## [1.8.1] - 2019-07-02
 
 ### Fixed