add sklearn in requirements.txt

requirements.txt

@@ -9,4 +9,5 @@ scipy
 scikit-learn==0.23.2
 gast==0.3.3
 faiss-cpu==1.7.1.post2
-bcolz==1.2.1
\ No newline at end of file
+bcolz==1.2.1
+scikit-learn==0.23.2
\ No newline at end of file