[SPARK-2861] Fix Doc comment of histogram method

Tested and ready to merge.

Author: Chandan Kumar <chandan.kumar@imaginea.com>

Closes apache#1786 from nrchandan/spark-2861 and squashes the following commits:

cb0bc1e [Chandan Kumar] [SPARK-2861] Fix a typo in the histogram doc comment
6a2a71b [Chandan Kumar] SPARK-2861. Fix Doc comment of histogram method

Author: Chandan Kumar

core/src/main/scala/org/apache/spark/rdd/DoubleRDDFunctions.scala

@@ -119,11 +119,11 @@ class DoubleRDDFunctions(self: RDD[Double]) extends Logging with Serializable {
 
   /**
    * Compute a histogram using the provided buckets. The buckets are all open
-   * to the left except for the last which is closed
+   * to the right except for the last which is closed
    *  e.g. for the array
    *  [1, 10, 20, 50] the buckets are [1, 10) [10, 20) [20, 50]
-   *  e.g 1<=x<10 , 10<=x<20, 20<=x<50
-   *  And on the input of 1 and 50 we would have a histogram of 1, 0, 0
+   *  e.g 1<=x<10 , 10<=x<20, 20<=x<=50
+   *  And on the input of 1 and 50 we would have a histogram of 1, 0, 1
    *
    * Note: if your histogram is evenly spaced (e.g. [0, 10, 20, 30]) this can be switched
    * from an O(log n) inseration to O(1) per element. (where n = # buckets) if you set evenBuckets