Update Changelog 2.1.4rc2

CHANGELOG.txt

@@ -1,4 +1,4 @@
-Airflow 2.1.4, 2021-09-15
+Airflow 2.1.4, 2021-09-18
 -------------------------
 
 Bug Fixes
@@ -27,6 +27,9 @@ Bug Fixes
 - Do not let ``create_dagrun`` overwrite explicit ``run_id`` (#17728)
 - BugFix: Regression on pid reset to allow task start after heartbeat (#17333)
 - Set task state to failed when pod is DELETED while running (#18095)
+- Advises the kernel to not cache log files generated by Airflow (#18054)
+- Sort adopted tasks in ``_check_for_stalled_adopted_tasks`` method (#18208)
+- Fix ``DagRunState`` enum query for ``MySQLdb`` driver (#17886)
 
 Doc only changes
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@@ -40,6 +43,9 @@ Doc only changes
 - Suggest to use secrets backend for variable when it contains sensitive data (#17319)
 - Improves quick-start docker-compose warnings and documentation (#18164)
 - Separate Installing from sources section and add more details (#18171)
+- Doc: Use ``closer.lua`` script for downloading sources (#18179)
+- Doc: Improve installing from sources (#18194)
+- Improves installing from sources pages for all components (#18251)
 
 Airflow 2.1.3, 2021-08-21
 -------------------------