Bump version to 2.6.0rc1 (#9025)

* Bump version to 2.6.0rc1

* Update AUTHORS.md

* Update CHANGELOG.md

lib/mastodon/version.rb

@@ -9,11 +9,11 @@ module Mastodon
     end
 
     def minor
-      5
+      6
     end
 
     def patch
-      2
+      0
     end
 
     def pre
@@ -21,7 +21,7 @@ module Mastodon
     end
 
     def flags
-      ''
+      'rc1'
     end
 
     def to_a