Update README.md (#1095)

Extra open brace in the .bibtex entry results in an error

README.md

@@ -192,7 +192,7 @@ If you use DGL in a scientific publication, we would appreciate citations to the
 @article{wang2019dgl,
     title={Deep Graph Library: Towards Efficient and Scalable Deep Learning on Graphs},
     url={https://arxiv.org/abs/1909.01315},
-    author={{Wang, Minjie and Yu, Lingfan and Zheng, Da and Gan, Quan and Gai, Yu and Ye, Zihao and Li, Mufei and Zhou, Jinjing and Huang, Qi and Ma, Chao and Huang, Ziyue and Guo, Qipeng and Zhang, Hao and Lin, Haibin and Zhao, Junbo and Li, Jinyang and Smola, Alexander J and Zhang, Zheng},
+    author={Wang, Minjie and Yu, Lingfan and Zheng, Da and Gan, Quan and Gai, Yu and Ye, Zihao and Li, Mufei and Zhou, Jinjing and Huang, Qi and Ma, Chao and Huang, Ziyue and Guo, Qipeng and Zhang, Hao and Lin, Haibin and Zhao, Junbo and Li, Jinyang and Smola, Alexander J and Zhang, Zheng},
     journal={ICLR Workshop on Representation Learning on Graphs and Manifolds},
     year={2019}
 }