Bump numpy from 1.17.4 to 1.21.0 in /examples/hyperparameter/LightGBM (#896)

Bumps [numpy](https://github.com/numpy/numpy) from 1.17.4 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/v1.17.4...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/hyperparameter/LightGBM/requirements.txt

@@ -1,5 +1,5 @@
 pandas==1.1.2
-numpy==1.17.4
+numpy==1.21.0
 lightgbm==3.1.0
 optuna==2.7.0
 optuna-dashboard==0.4.1