mark version (#836)

Co-authored-by: LasNikas <niklas.nehe@web.de>
Co-authored-by: Erik Faulhaber <44124897+efaulhaber@users.noreply.github.com>

Author: 3 people

Project.toml

@@ -1,7 +1,7 @@
 name = "TrixiParticles"
 uuid = "66699cd8-9c01-4e9d-a059-b96c86d16b3a"
 authors = ["erik.faulhaber <44124897+efaulhaber@users.noreply.github.com>"]
-version = "0.3.1-dev"
+version = "0.3.1"
 
 [deps]
 Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"