Upgrade fluency-meter-registry to support old fluentd (treasure-data#…

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* Upgrade fluency-meter-registry to support old fluentd.

* Fix an integration test for fluency metrics.

0.9.38

ver. 0.9.37

Merge pull request treasure-data#1046 from yoyama/release_v0.9.35

Prepare for 0.9.35

Merge pull request treasure-data#1035 from yoyama/release_0.9.34

Prepare for release 0.9.34

Merge pull request treasure-data#986 from yoyama/release_0.9.33

Prepare for release 0.9.33

Release v0.9.32

Release v0.9.31