Update CHANGELOG.md

Merge pull request influxdata#2479 from influxdata/fix-influx-writes

fix: influx gzip writes

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Merge pull request influxdata#2464 from influxdata/rem-386

Remove darwin/arm64 build as it doesn't actually work till go1.16

Merge pull request influxdata#2462 from influxdata/rem-386

chore: remove 386 darwin support and add arm64 darwin

Merge pull request influxdata#2461 from influxdata/rem-386

chore: remove support for 386

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Merge pull request influxdata#2414 from rhajek/feat/bigpanda

Feat/Big Panda Event Handler

Merge pull request influxdata#2423 from influxdata/docmerlin-patch-1

Update Changelog for 1.5.7 release.