!906 upgrade the version of scikit-learn to 0.23.1

From: @luopengting
Reviewed-by: @ouwenchang,@wenkai_dist
Signed-off-by: @wenkai_dist

requirements.txt

@@ -13,7 +13,7 @@ protobuf>=3.8.0
 psutil>=5.6.1
 pyyaml>=5.3.1
 scipy>=1.5.3
-scikit-learn>=0.21.2
+scikit-learn>=0.23.1
 six>=1.12.0
 Werkzeug>=1.0.0
 pandas>=1.0.4