Created by: kexinzhao

https://github.com/PaddlePaddle/Paddle/blob/35572355c2261c493aa782ba1255971f4dfa385e/paddle/operators/rank_loss_op.cc#L71-L75

\f should be removed.

Correctly, it is incorrectly displayed here: http://www.paddlepaddle.org/docs/develop/documentation/en/operators.html#permalink-82-rank_loss