Update CITATION from Workshop paper to Conference paper (#30872)
Summary:
The conference paper is finally published at NeurIPS 2019: http://papers.neurips.cc/paper/9015-pytorch-an-imperative-style-high-performance-deep-learning-library.pdf
Pull Request resolved: https://github.com/pytorch/pytorch/pull/30872
Differential Revision: D18854253
Pulled By: soumith
fbshipit-source-id: 4f91838b1953e976542997959d5571884f739872
