ignore data files in .gitignore

Summary: Pull Request resolved: https://github.com/pytorch/fairseq/pull/546

Differential Revision: D14272808

Pulled By: myleott

fbshipit-source-id: e993450354e7d7561b14b56c12d4859a8ee7121b

.gitignore

@@ -108,3 +108,6 @@ ENV/
 
 # Generated files
 fairseq/temporal_convolution_tbc
+
+# data
+data-bin/

preprocess.py

@@ -26,6 +26,7 @@ def main(args):
     import_user_module(args)
 
     print(args)
+
     os.makedirs(args.destdir, exist_ok=True)
     target = not args.only_source