Updates v1.1.1 release date

Author: LordHepipud

doc/31-Changelog.md

@@ -7,7 +7,7 @@ documentation before upgrading to a new release.
 
 Released closed milestones can be found on [GitHub](https://github.com/Icinga/icinga-powershell-framework/milestones?state=closed).
 
-## 1.1.1 (2020-06-30)
+## 1.1.1 (2020-06-18)
 
 [Issue and PRs](https://github.com/Icinga/icinga-powershell-framework/milestone/8?closed=1)