Update transformers requirement from <4.15,>=4.1 to >=4.1,<4.16 (#5528)

Updates the requirements on [transformers](https://github.com/huggingface/transformers) to permit the latest version.
- [Release notes](https://github.com/huggingface/transformers/releases)
- [Commits](huggingface/transformers@v4.1.0...v4.15.0)

---
updated-dependencies:
- dependency-name: transformers
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Pete <petew@allenai.org>

setup.py

@@ -65,7 +65,7 @@
         "scikit-learn",
         "scipy",
         "pytest",
-        "transformers>=4.1,<4.15",
+        "transformers>=4.1,<4.16",
         "sentencepiece",
         "dataclasses;python_version<'3.7'",
         "filelock>=3.3,<3.5",