bump changelog version

CHANGELOG.md

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 # Changelog
 All notable changes to Oragono will be documented in this file.
 
-## [2.2.0-rc1] - 2020-07-19
+## [2.2.0] - 2020-07-26
 
-We're pleased to be publishing the release candidate for 2.2.0 (the official release should follow in a week or so).
+We're pleased to announce Oragono 2.2.0, a new stable release.
 
 This release contains several notable enhancements, as well as bug fixes: