Fix v2020.6 release notes schedule

Fix minor issue in v2020.6 release notes about the support of v2021.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>

content/release/v2020.6/releasenotes.md

@@ -12,7 +12,8 @@ systems.
 
 **Apertis v2020.6** is the seventh **stable** release of the Apertis
 v2020 [release flow]( {{< ref "release-flow.md#apertis-release-flow" >}} ).
-Apertis is committed to maintaining the v2020 release stream until September 2021.
+Apertis is committed to maintaining the v2020 release stream until the end of
+2021.
 
 This Apertis release is built on top of Debian Buster with several
 customisations and the Linux kernel 5.4.x LTS series.