Bump version to 0.3.1

ecs_core/__init__.py

-__version__ = '0.3.0'
+__version__ = '0.3.1'

pyproject.toml

 [tool.poetry]
 name = "ecs-core"
-version = "0.3.0"
+version = "0.3.1"
 description = "Core agents of the CBM ECS"
 authors = ["P.-A. Loizeau"]
 license = "GPL-3.0-only"

tests/test_ecs_core.py

@@ -2,4 +2,4 @@ from ecs_core import __version__
 
 
 def test_version() -> None:
-    assert __version__ == '0.3.0'
+    assert __version__ == '0.3.1'