Rename package gradient to optimization

ml/src/main/scala/spark/ml/gradient/Gradient.scala → ml/src/main/scala/spark/ml/optimization/Gradient.scala

-package spark.ml.gradient
+package spark.ml.optimization
 
 import org.jblas.DoubleMatrix
 

ml/src/main/scala/spark/ml/gradient/GradientDescent.scala → ml/src/main/scala/spark/ml/optimization/GradientDescent.scala

-package spark.ml.gradient
+package spark.ml.optimization
 
 import spark.{Logging, RDD, SparkContext}
 import spark.SparkContext._

ml/src/main/scala/spark/ml/gradient/Updater.scala → ml/src/main/scala/spark/ml/optimization/Updater.scala

-package spark.ml.gradient
+package spark.ml.optimization
 
 import org.jblas.DoubleMatrix
 

ml/src/main/scala/spark/ml/regression/LogisticRegression.scala

 package spark.ml.regression
 
 import spark.{Logging, RDD, SparkContext}
-import spark.ml.gradient._
+import spark.ml.optimization._
 import spark.ml.util.MLUtils
 
 import org.jblas.DoubleMatrix