[SPARK-14058][PYTHON] Incorrect docstring in Window.order

## What changes were proposed in this pull request?

Replaces current docstring ("Creates a :class:`WindowSpec` with the partitioning defined.") with "Creates a :class:`WindowSpec` with the ordering defined."

## How was this patch tested?

PySpark unit tests (no regression introduced). No changes to the code.

Author: zero323 <matthew.szymkiewicz@gmail.com>

Closes #11877 from zero323/order-by-description.

(cherry picked from commit 8193a26)
Signed-off-by: Reynold Xin <rxin@databricks.com>

Author: zero323

python/pyspark/sql/window.py

@@ -60,7 +60,7 @@ def partitionBy(*cols):
     @since(1.4)
     def orderBy(*cols):
         """
-        Creates a :class:`WindowSpec` with the partitioning defined.
+        Creates a :class:`WindowSpec` with the ordering defined.
         """
         sc = SparkContext._active_spark_context
         jspec = sc._jvm.org.apache.spark.sql.expressions.Window.orderBy(_to_java_cols(cols))