Revert "Pin bundler version to 2.2.3 (#310)" (#311)
Revert "Pin bundler version to 2.2.3 (#310)" (#311)

This reverts commit a473b50d6ccd50960429de86b01ce51a073ec62a.
GoogleCloudPlatform/google-fluentd,GoogleCloudPlatform/google-fluentd,GoogleCloudPlatform/google-fluentd