Update CHANGELOG.md

Add #378

Signed-off-by: Ben Kochie <superq@gmail.com>

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 Deprecation notice: The comma delimited flags `google.project-id` and `monitoring.metrics-type-prefixes` are being replaced by repeatable flags `google.project-ids` and `monitoring.metrics-prefixes`. The comma delimited flags will be supported for at least one more release. 
 
+- [CHANGE] Migrate logging to promslog #378
 - [ENHANCEMENT] Sanitize metric type prefixes to prevent duplicate metrics #319
 - [ENHANCEMENT] Add project ID to all logs from the collector #362
 - [FEATURE] Add support for specifying comma-delimited string flags as repeatable flags #355