Add a line in changelog about retry plugin async

Author: joelwurtz

Diff for: CHANGELOG.md

@@ -9,6 +9,7 @@
 ### Changed
 
 - AddPathPlugin no longer add prefix multiple times if a request is restarted - it now only adds the prefix if that request chain has not yet passed through the AddPathPlugin
+- RetryPlugin no longer wait for retried requests and use a deferred promise instead
 
 ## 1.7.0 - 2017-11-30