Bump numpy from 1.19.2 to 1.21.0 in /examples/research_projects/lxmert (#15369)

Bumps [numpy](https://github.com/numpy/numpy) from 1.19.2 to 1.21.0.
- [Release notes](https://github.com/numpy/numpy/releases)
- [Changelog](https://github.com/numpy/numpy/blob/main/doc/HOWTO_RELEASE.rst.txt)
- [Commits](https://github.com/numpy/numpy/compare/v1.19.2...v1.21.0

)

---
updated-dependencies:
- dependency-name: numpy
  dependency-type: direct:production
...
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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

examples/research_projects/lxmert/requirements.txt

@@ -47,7 +47,7 @@ nbconvert==6.0.1
 nbformat==5.0.7
 nest-asyncio==1.4.0
 notebook==6.4.1
-numpy==1.19.2
+numpy==1.21.0
 opencv-python==4.4.0.42
 packaging==20.3
 pandas==1.1.2