patch ernie-gen path

ernie-gen/README.md

+```bash
+ _____ ____  _   _ ___ _____       ____ _____ _   _ 
+| ____|  _ \| \ | |_ _| ____|     / ___| ____| \ | |
+|  _| | |_) |  \| || ||  _| _____| |  _|  _| |  \| |
+| |___|  _ <| |\  || || |__|_____| |_| | |___| |\  |
+|_____|_| \_\_| \_|___|_____|     \____|_____|_| \_|
+```
+
+The `ERNIE-GEN` (including all our pre-trained models) has been released at [here](https://github.com/PaddlePaddle/ERNIE/tree/repro/ernie-gen).