Update tensorboardx requirement from <2.3,>=2.1 to >=2.1,<2.4 (#163)

Updates the requirements on [tensorboardx](https://github.com/lanpa/tensorboardX) to permit the latest version.
- [Release notes](https://github.com/lanpa/tensorboardX/releases)
- [Changelog](https://github.com/lanpa/tensorboardX/blob/master/HISTORY.rst)
- [Commits](https://github.com/lanpa/tensorboardX/commits)

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

Signed-off-by: dependabot[bot] <[email protected]>

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

setup.py

@@ -48,7 +48,7 @@
         'numpy>=1.14.5',
         'torch~=1.7.1',
         'tqdm==4.49.0',
-        'tensorboardX>=2.1,<2.3',
+        'tensorboardX>=2.1,<2.4',
         'pyrouge>=0.1.3',
         'sacrebleu~=1.0',
         'bert-score~=0.3',