Update parameter.md

doc/parameter.md

@@ -56,7 +56,7 @@ From xgboost-unity, the ```bst:``` prefix is no longer needed for booster parame
  - "binary:logistic" --logistic regression for binary classification, output probability
  - "binary:logitraw" --logistic regression for binary classification, output score before logistic transformation
  - "count:poisson" --poisson regression for count data, output mean of poisson distribution
-   - max_delta_step is set to 1 by default in poisson regression(used to safeguard optimization)
+   - max_delta_step is set to 0.7 by default in poisson regression (used to safeguard optimization)
  - "multi:softmax" --set XGBoost to do multiclass classification using the softmax objective, you also need to set num_class(number of classes)
  - "multi:softprob" --same as softmax, but output a vector of ndata * nclass, which can be further reshaped to ndata, nclass matrix. The result contains predicted probability of each data point belonging to each class.
  - "rank:pairwise" --set XGBoost to do ranking task by minimizing the pairwise loss