Twitter-oss: update OSS libraries post-release to 21.9.0

Problem

We want to update to the next SNAPSHOT version of our Twitter OSS libraries 21.9.0
 - util
 - scrooge
 - finagle
 - twitter-server
 - finatra

Solution

Prepare libraries for their next SNAPSHOT version.

JIRA Issues: CSL-11162

Differential Revision: https://phabricator.twitter.biz/D722646

README.md

@@ -1,6 +1,6 @@
 # TwitterServer
 
-[![Build Status](https://github.com/twitter/twitter-server/workflows/continuous%20integration/badge.svg?branch=release)](https://github.com/twitter/twitter-server/actions?query=workflow%3A%22continuous+integration%22+branch%3Arelease)
+[![Build Status](https://github.com/twitter/twitter-server/workflows/continuous%20integration/badge.svg?branch=develop)](https://github.com/twitter/twitter-server/actions?query=workflow%3A%22continuous+integration%22+branch%3Adevelop)
 [![Codecov](https://codecov.io/gh/twitter/twitter-server/branch/develop/graph/badge.svg)](https://codecov.io/gh/twitter/twitter-server)
 [![Project status](https://img.shields.io/badge/status-active-brightgreen.svg)](#status)
 [![Gitter](https://badges.gitter.im/twitter/finagle.svg)](https://gitter.im/twitter/finagle?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)

build.sbt

@@ -4,7 +4,7 @@ Global / onChangedBuildSource := ReloadOnSourceChanges
 Global / excludeLintKeys += scalacOptions
 
 // All Twitter library releases are date versioned as YY.MM.patch
-val releaseVersion = "21.8.0"
+val releaseVersion = "21.9.0-SNAPSHOT"
 
 val jacksonVersion = "2.11.2"
 val jacksonLibs = Seq(