Log Message:
mikutter: update to 5.0.6.

Upstream changes:
 https://mikutter.hatenablog.com/entry/2024/03/16/150527

mikutter 5.0.6

* lint by rubocop against newer sources and reorganize sources
* remove twitter_api_keys plugin
 * thanks Izumi Tsutsui
* use gtk3 4.2.1
 * thanks Izumi Tsutsui
* thumbnails of niconico-video were not shown
 * thanks Izumi Tsutsui
* remove unused oauth gem from Gemfile
 * thanks Izumi Tsutsui