fix wrong var name in OSFS.getinfo() conversion of st_mtime => modified_time

fs/osfs.py

@@ -217,7 +217,7 @@ class OSFS(FS):
             info['accessed_time'] = datetime.datetime.fromtimestamp(at)
         mt = info.get('st_mtime', None)
         if mt is not None:
-            info['modified_time'] = datetime.datetime.fromtimestamp(at)
+            info['modified_time'] = datetime.datetime.fromtimestamp(mt)
         return info
 
     @convert_os_errors