Add sacrebleu to requirements

Summary: Pull Request resolved: https://github.com/pytorch/fairseq/pull/542

Differential Revision: D14258895

Pulled By: myleott

fbshipit-source-id: 950a840e1d001a472be8d4737c9e4de5224137b3

setup.py

@@ -42,6 +42,7 @@ setup(
     install_requires=[
         'cffi',
         'numpy',
+        'sacrebleu',
         # don't include torch, to support both release and nightly builds
         #'torch',
         'tqdm',