Update files from the datasets library (from 1.6.0)

Release notes: https://github.com/huggingface/datasets/releases/tag/1.6.0

README.md

@@ -11,7 +11,7 @@ licenses:
 multilinguality:
 - monolingual
 size_categories:
-- n>1M
+- 1M<n<10M
 source_datasets:
 - original
 task_categories:

wikitext_tl39.py

@@ -1,6 +1,5 @@
 """TODO(wikitext): Add a description here."""
 
-from __future__ import absolute_import, division, print_function
 
 import os