README: adjust calver to MAJOR.MINOR.[MICRO]

Make the micro patchlevel optional.

Signed-off-by: Rouven Czerwinski <[email protected]>

Author: Emantor

README.rst

@@ -123,6 +123,6 @@ Tests can now run via:
     :alt: chat
     :target: https://app.element.io/#/room/#labgrid:matrix.org
 
-.. |calver| image:: https://img.shields.io/badge/calver-YY.MINOR.MICRO-22bfda.svg 
+.. |calver| image:: https://img.shields.io/badge/calver-YY.MINOR.%5BMICRO%5D-22bfda.svg
     :alt: chat
     :target: https://calver.org/