Clarify that returning None is an interface (+fix a typo)

Author: tkf

julia/core.py

@@ -287,7 +287,8 @@ def linked_libpython(path):
         return libpython_from_ldd_output(subprocess.check_output(
             ["ldd", path],
             universal_newlines=True))
-# TODO: somebody has to write it for in Windows and macOS:
+    return None
+# TODO: somebody has to write it for Windows and macOS:
 
 
 JuliaInfo = namedtuple(