Fix release date for 2.1.1 (apache#16788)

Airflow 2.1.1 was released a bit later than we expected, it was released on 2021-07-02

Author: kaxil

CHANGELOG.txt

@@ -1,10 +1,9 @@
-Airflow 2.1.1, 2021-06-29
+Airflow 2.1.1, 2021-07-02
 -------------------------
 
 Bug Fixes
 """""""""
 
-
 - Don't crash attempting to mask secrets in dict with non-string keys (#16601)
 - Always install sphinx_airflow_theme from ``PyPI`` (#16594)
 - Remove limitation for elasticsearch library (#16553)