update java train-validation-split example in ml-guide

Author: JeremyNixon

docs/ml-guide.md

@@ -913,7 +913,7 @@ import org.apache.spark.ml.regression.LinearRegression;
 import org.apache.spark.ml.tuning.*;
 import org.apache.spark.sql.DataFrame;
 
-DataFrame data = jsql.read().format("libsvm").load("data/mllib/sample_libsvm_data.txt");
+DataFrame data = jsql.read().format("libsvm").load("data/mllib/sample_linear_regression_data.txt");
 
 // Prepare training and test data.
 DataFrame[] splits = data.randomSplit(new double[] {0.9, 0.1}, 12345);