fix: folder/Base: missing """ for doc string

Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/folder/Base.py

@@ -197,7 +197,7 @@ class BaseFolder(object):
             return True
 
     def _getuidfilename(self):
-        """provides UIDVALIDITY cache filename for class internal purposes.
+        """provides UIDVALIDITY cache filename for class internal purposes."""
 
         return os.path.join(self.repository.getuiddir(),
                             self.getfolderbasename())