Bump xgboost from 1.2.0 to 1.2.1 (#1860)

Bumps [xgboost](https://github.com/dmlc/xgboost) from 1.2.0 to 1.2.1.
- [Release notes](https://github.com/dmlc/xgboost/releases)
- [Changelog](https://github.com/dmlc/xgboost/blob/master/NEWS.md)
- [Commits](https://github.com/dmlc/xgboost/compare/v1.2.0...v1.2.1)

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requirements.txt

@@ -26,5 +26,5 @@ tabulate==0.8.7
 taskcluster==37.3.0
 tenacity==6.2.0
 tqdm==4.50.2
-xgboost==1.2.0
+xgboost==1.2.1
 zstandard==0.14.0