update scikit-learn in requirement.txt

requirements.txt

@@ -4,9 +4,8 @@ opencv-python==4.4.0.46
 pillow
 tqdm
 PyYAML
-visualdl >= 2.2.0
+visualdl>=2.2.0
 scipy
-scikit-learn==0.23.2
+scikit-learn>=0.21.0
 gast==0.3.3
 faiss-cpu==1.7.1.post2
-scikit-learn==0.23.2
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