Prepare changelog for 91 release

Author: csadilek

docs/changelog.md

@@ -4,12 +4,12 @@ title: Changelog
 permalink: /changelog/
 ---
 
-# 91.0.0-SNAPSHOT (In Development)
-* [Commits](https://github.com/mozilla-mobile/android-components/compare/v90.0.0...master)
+# 91.0.0
+* [Commits](https://github.com/mozilla-mobile/android-components/compare/v91.0.0...master)
 * [Milestone](https://github.com/mozilla-mobile/android-components/milestone/138?closed=1)
-* [Dependencies](https://github.com/mozilla-mobile/android-components/blob/master/buildSrc/src/main/java/Dependencies.kt)
-* [Gecko](https://github.com/mozilla-mobile/android-components/blob/master/buildSrc/src/main/java/Gecko.kt)
-* [Configuration](https://github.com/mozilla-mobile/android-components/blob/master/.config.yml)
+* [Dependencies](https://github.com/mozilla-mobile/android-components/blob/v91.0.0/buildSrc/src/main/java/Dependencies.kt)
+* [Gecko](https://github.com/mozilla-mobile/android-components/blob/v90.0.0/buildSrc/src/main/java/Gecko.kt)
+* [Configuration](https://github.com/mozilla-mobile/android-components/blob/v91.0.0/.config.yml)
 
 * **browser-errorpages**:
   * `ErrorType.ERROR_SECURITY_SSL` will now no longer display `Advanced` button on the SSL Error Page.