Fix: Version string test case

pystencils_tests/test_version_string.py

-import lbmpy
+import pystencils as ps
 
 
 def test_version_string():
-    version = lbmpy.__version__
+    version = ps.__version__
     print(version)
 
     numeric_version = [int(x, 10) for x in version.split('.')[0:1]]