fix(identify): actually send $set_once on identify calls

[hazzadous]

We were handling $set but not $set_once. This fixes that.

Fixes #615

Changes

...

Checklist

• Tests for new code (see advice on the tests we use)
• Accounted for the impact of any changes across different browsers

[github-actions]

Size Change: +64 B (0%)

Total Size: 2.32 MB

Filename	Size	Change
dist/array.full.js	160 kB	+16 B (0%)
dist/array.js	102 kB	+16 B (0%)
dist/es.js	101 kB	+16 B (0%)
dist/module.js	102 kB	+16 B (0%)

ℹ️ View Unchanged

Filename	Size
dist/recorder-v2.js	93.6 kB
dist/recorder.js	58.3 kB
lib/rrweb/dist/plugins/console-record.js	26.6 kB
lib/rrweb/dist/plugins/console-record.min.js	10.8 kB
lib/rrweb/dist/plugins/console-replay.js	12.7 kB
lib/rrweb/dist/plugins/console-replay.min.js	5.72 kB
lib/rrweb/dist/plugins/sequential-id-record.js	910 B
lib/rrweb/dist/plugins/sequential-id-record.min.js	417 B
lib/rrweb/dist/plugins/sequential-id-replay.js	1.24 kB
lib/rrweb/dist/plugins/sequential-id-replay.min.js	578 B
lib/rrweb/dist/record/rrweb-record-pack.js	31.4 kB
lib/rrweb/dist/record/rrweb-record-pack.min.js	10.7 kB
lib/rrweb/dist/record/rrweb-record.js	140 kB
lib/rrweb/dist/record/rrweb-record.min.js	51.7 kB
lib/rrweb/dist/replay/rrweb-replay-unpack.js	188 kB
lib/rrweb/dist/replay/rrweb-replay-unpack.min.js	71.1 kB
lib/rrweb/dist/replay/rrweb-replay.js	172 kB
lib/rrweb/dist/replay/rrweb-replay.min.js	66.4 kB
lib/rrweb/dist/rrweb-all.js	356 kB
lib/rrweb/dist/rrweb-all.min.js	133 kB
lib/rrweb/dist/rrweb.js	302 kB
lib/rrweb/dist/rrweb.min.js	116 kB
lib/rrweb/es/rrweb/ext/base64-arraybuffer/dist/base64-arraybuffer.es5.js	1.94 kB
lib/rrweb/es/rrweb/ext/mitt/dist/mitt.es.js	1.99 kB

_{compressed-size-action}

[tiina303]

lgtm