Bump version to 0.5.3

pyproject.toml

 [tool.poetry]
 name = "calendarweek"
-version = "0.5.2"
+version = "0.5.3"
 description = "Utilities for working with calendar weeks in Python and Django"
 authors = ["Dominik George <nik@naturalnet.de>", "Jonathan Weth <git@jonathanweth.de>"]
 license = "Apache-2.0"