finagle|finatra|scrooge|twitter-server|util: 3rd party upgrade cadenc…

…e note

Problem/Solution

We agreed to upgrade Netty, Guice, Jackson, Caffeine, & sbt on a quarterly
cadence. We should communicate this in our `CONTRIBUTING.md` docs.

JIRA Issues: CSL-11166

Differential Revision: https://phabricator.twitter.biz/D704594

CONTRIBUTING.md

@@ -35,6 +35,14 @@ If you have any questions or run into any problems, please create
 an issue here, chat with us in [gitter](https://gitter.im/twitter/finagle), or email
 the Finaglers [mailing list](https://groups.google.com/forum/#!forum/finaglers).
 
+### 3rd party upgrades
+
+We upgrade the following 3rd party libraries/tools at least once every 3 months:
+* [sbt](https://github.com/sbt/sbt)
+* [Netty](https://github.com/netty/netty)
+* [Jackson](https://github.com/FasterXML/jackson)
+* [Caffeine](https://github.com/ben-manes/caffeine)
+
 ## Workflow
 
 The workflow that we support: