fix import error (#41)

src/actinia_statistic_plugin/__init__.py

@@ -1,9 +1,9 @@
 # -*- coding: utf-8 -*-
-from pkg_resources import get_distribution, DistributionNotFound
+import importlib.metadata
 
 try:
     # Change here if project is renamed and does not equal the package name
     dist_name = __name__
-    __version__ = get_distribution(dist_name).version
-except DistributionNotFound:
+    __version__ = importlib.metadata.version(dist_name)
+except Exception:
     __version__ = "unknown"