Release 0.1.1 - 2023/07/12

 * CI: Update supported version of Ruby.
   - Ruby 2.6 was dropped
 * CI: Add GitHub Action to watch by dependabot (weekly).
 * Stay on prometheus-client to 2.1.0.
 * Relax required version of fluent-plugin-prometheus to 2.1.0.

Release 0.1.0 - 2021/04/20

　* Upgrade fluent-plugin-prometheus to 2.0

