Convert os.Pathlike objects to string so it also works on Python 3.5

Author: Janneke van der Zwaan

tests/test_library.py

@@ -11,13 +11,13 @@
 
 @pytest.mark.datafiles(Path(data_dir) / 'align-dir-pack.cwl')
 def test_load_yaml_packed(datafiles):
-    cwl_file = datafiles.listdir()[0]
+    cwl_file = str(datafiles.listdir()[0])
 
     assert {} == load_yaml(cwl_file)
 
 
 @pytest.mark.datafiles(Path(data_dir) / 'align-dir-pack.cwl')
 def test_load_steps_file_packed(datafiles):
-    cwl_file = datafiles.listdir()[0]
+    cwl_file = str(datafiles.listdir()[0])
 
     assert {} == load_steps(step_file=cwl_file)