Update async-emitter link in docs

doc/development/snowplow/index.md

@@ -427,7 +427,7 @@ https://docs.gitlab.com/ee/development/testing_guide/best_practices.html#test-sn
 
 ### Performance
 
-We use the [AsyncEmitter](https://github.com/snowplow/snowplow/wiki/Ruby-Tracker#52-the-asyncemitter-class) when tracking events, which allows for instrumentation calls to be run in a background thread. This is still an active area of development.
+We use the [AsyncEmitter](https://docs.snowplowanalytics.com/docs/collecting-data/collecting-from-own-applications/ruby-tracker/emitters/#the-asyncemitter-class) when tracking events, which allows for instrumentation calls to be run in a background thread. This is still an active area of development.
 
 ## Developing and testing Snowplow