title: How to specify positive label when use precision as scoring in GridSearchCV
body: <pre><code>model = sklearn.model_selection.GridSearchCV(
          estimator = est, 
          param_grid = param_grid,
          scoring = 'precision',
          verbose = 1,
          n_jobs = 1,
          iid = True,
          cv = 3)
  </code></pre>
  
  <p>In <code>sklearn.metrics.precision_score(y, y_pred,pos_label=[0])</code>, I can specify the positive label, how can I specify this in GridSearchCV too?</p>
  
  <p>If there is no way to specify, when using custom scoring, how can I define?  </p>
  
  <p>I have tried this:  </p>
  
  <pre><code>custom_score = make_scorer(precision_score(y, y_pred,pos_label=[0]),  
                            greater_is_better=True)  
  </code></pre>
  
  <p>but I got error: </p>
  
  <pre><code>NameError: name 'y_pred' is not defined
  </code></pre>