Fixes path bug in shed meta file creation

pydtn/shed.py

@@ -31,7 +31,10 @@ def write_meta_file(meta_path, csv_path, duty_cycle_length=300):
             nodes.add(target)
             last = max(last, int(slot))
 
-    common = path.commonprefix([meta_path, csv_path])
+    common = path.commonprefix([
+        path.dirname(meta_path),
+        path.dirname(csv_path),
+    ])
     csv_path = path.relpath(csv_path, common)
 
     meta_data = {