fix docstring problem

Author: huaxingao

python/pyspark/ml/classification.py

@@ -1301,7 +1301,7 @@ def setParams(self, featuresCol="features", labelCol="label", predictionCol="pre
                   maxDepth=5, maxBins=32, minInstancesPerNode=1, minInfoGain=0.0, \
                   maxMemoryInMB=256, cacheNodeIds=False, checkpointInterval=10, \
                   lossType="logistic", maxIter=20, stepSize=0.1, seed=None, subsamplingRate=1.0, \
-                  impurity="variance", featureSubsetStrategy="all", validationTol=0.01,
+                  impurity="variance", featureSubsetStrategy="all", validationTol=0.01, \
                   validationIndicatorCol=None)
         Sets params for Gradient Boosted Tree Classification.
         """