Update grid_search.py (#79)

Fix `best_params_` not being set after a call to `fit`. This resolves issue #73

Author: Kautenja

python/spark_sklearn/grid_search.py

@@ -369,6 +369,7 @@ def _store(key_name, array, weights=None, splits=False, rank=False):
 
         best_index = np.flatnonzero(results["rank_test_score"] == 1)[0]
         best_parameters = candidate_params[best_index]
+        self.best_params_ = best_parameters
 
         # Use one MaskedArray and mask all the places where the param is not
         # applicable for that candidate. Use defaultdict as each candidate may