Update gems

This MR contains the following updates:

Package	Update	Change
fluent-plugin-elasticsearch	minor	~> 4.2.0 -> ~> 4.3.0
fluent-plugin-kubernetes_metadata_filter	minor	~> 2.5.0 -> ~> 2.6.0
fluent-plugin-rewrite-tag-filter	minor	~> 2.3.0 -> ~> 2.4.0
fluentd	minor	1.11.4 -> 1.12.1
oj	minor	3.10.15 -> 3.11.3

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