Stubbed CHANGELOG for version 0.4.0
Stubbed CHANGELOG for version 0.4.0

RetentionGrid/snowplow-ruby-tracker,snowplow/snowplow-ruby-tracker,liveintent-berlin/snowplow-ruby-tracker,snowplow/snowplow-ruby-tracker,liveintent-berlin/snowplow-ruby-tracker,RetentionGrid/snowplow-ruby-tracker