update typo in FeatureEngineering (#2292)

docs/en_US/FeatureEngineering/Overview.md

@@ -148,7 +148,7 @@ from sklearn.feature_selection.base import SelectorMixin
 
 from nni.feature_engineering.feature_selector import FeatureSelector
 
-class CustomizedSelector(FeatureSelector, BaseEstimator):
+class CustomizedSelector(FeatureSelector, BaseEstimator, SelectorMixin):
     def __init__(self, ...):
         ...
     
@@ -161,7 +161,7 @@ class CustomizedSelector(FeatureSelector, BaseEstimator):
         if not key.endswith('_')}
         return params
         
-        def set_params(self, **params):
+    def set_params(self, **params):
         """
         Set the parameters of this estimator.
         """