Twitter-oss: Prepare OSS libraries for release 21.4

Problem

We want to release the next versions of our Twitter OSS libraries 21.4.0
 - util
 - scrooge
 - finagle
 - twitter-server
 - finatra

Solution

Prepare libraries for their next releases.

JIRA Issues: CSL-10889

Differential Revision: https://phabricator.twitter.biz/D658986

CHANGELOG.rst

@@ -7,6 +7,9 @@ Note that ``PHAB_ID=#`` and ``RB_ID=#`` correspond to associated messages in com
 Unreleased
 ----------
 
+21.4.0
+------
+
 * Change Metrics Metadata Endpoint to return a histogram's metadata when queried using the /admin/metrics.json
   full (suffixed) histogram name as the value for the name argument. ``PHAB_ID=D640725``
 

README.md

@@ -1,6 +1,6 @@
 # TwitterServer
 
-[![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)
+[![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)
 [![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

@@ -1,7 +1,7 @@
 import scoverage.ScoverageKeys
 
 // All Twitter library releases are date versioned as YY.MM.patch
-val releaseVersion = "21.4.0-SNAPSHOT"
+val releaseVersion = "21.4.0"
 
 val jacksonVersion = "2.11.2"
 val jacksonLibs = Seq(