Fix version number in setup.py

With version 0.21.0 support for python 2.7 is removed, support for more
versions of django and celery has been added.
Support for python 3.9 in CI and python 3.10 local has been added.
pg_wheel extra has been removed

HISTORY.rst

@@ -1,3 +1,22 @@
+0.21.0 (2021-09-24)
+-------------------
+
+* Drop python 2.7
+* Support more django versions
+* Support more Celery versions
+* Add tests for python 3.9 and local tests for python 3.10
+* Remove travis tests
+* Remove the pg_wheel extra target
+
+0.20.0 (2021-09-21)
+-------------------
+
+* Added support for python 3.7 and 3.8
+* Added support for celery => 5
+* Send more details (view-name) to sentry, for better grouping
+* Fix util.Local sorage thread safety, and include unittest
+* Last version to support python 2.7
+
 0.19.0 (2020-09-07)
 -------------------
 

setup.py

@@ -204,6 +204,6 @@
     ],
     test_suite='tests',
     url='https://github.com/canonical-ols/talisker',
-    version='0.20.0',
+    version='0.21.0',
     zip_safe=False,
 )