[SPARK-9198] [MLLIB] [PYTHON] Fixed typo in pyspark sparsevector doc tests

Several places in the PySpark SparseVector docs have one defined as:
```
SparseVector(4, [2, 4], [1.0, 2.0])
```
The index 4 goes out of bounds (but this is not checked).

CC: mengxr

Author: Joseph K. Bradley <[email protected]>

Closes #7541 from jkbradley/sparsevec-doc-typo-fix and squashes the following commits:

c806a65 [Joseph K. Bradley] fixed doc test
e2dcb23 [Joseph K. Bradley] Fixed typo in pyspark sparsevector doc tests

(cherry picked from commit a5d0581)
Signed-off-by: Xiangrui Meng <[email protected]>

Author: jkbradley

python/pyspark/mllib/linalg.py

@@ -502,7 +502,7 @@ def dot(self, other):
         25.0
         >>> a.dot(array.array('d', [1., 2., 3., 4.]))
         22.0
-        >>> b = SparseVector(4, [2, 4], [1.0, 2.0])
+        >>> b = SparseVector(4, [2], [1.0])
         >>> a.dot(b)
         0.0
         >>> a.dot(np.array([[1, 1], [2, 2], [3, 3], [4, 4]]))
@@ -567,11 +567,11 @@ def squared_distance(self, other):
         11.0
         >>> a.squared_distance(np.array([1., 2., 3., 4.]))
         11.0
-        >>> b = SparseVector(4, [2, 4], [1.0, 2.0])
+        >>> b = SparseVector(4, [2], [1.0])
         >>> a.squared_distance(b)
-        30.0
+        26.0
         >>> b.squared_distance(a)
-        30.0
+        26.0
         >>> b.squared_distance([1., 2.])
         Traceback (most recent call last):
             ...