Fix arg formatting in preprocess.py and add fmt control for black formatting (#399)

Summary:
Not switching to Black formatting just yet, but adding fmt: off directives in case we decide to later.
Pull Request resolved: https://github.com/pytorch/fairseq/pull/399

Differential Revision: D13364674

Pulled By: myleott

fbshipit-source-id: a20a11a18be3d583ee30eff770278fb4bd05b93c

scripts/read_binarized.py

@@ -16,8 +16,10 @@ from fairseq.data import IndexedDataset
 def get_parser():
     parser = argparse.ArgumentParser(
         description='writes text from binarized file to stdout')
+    # fmt: off
     parser.add_argument('--dict', metavar='FP', required=True, help='dictionary containing known words')
     parser.add_argument('--input', metavar='FP', required=True, help='binarized file to read')
+    # fmt: on
 
     return parser