[SPARK-11670] Fix incorrect kryo buffer default value in docs
[SPARK-11670] Fix incorrect kryo buffer default value in docs

<img width="931" alt="screen shot 2015-11-11 at 1 53 21 pm" src="https://cloud.githubusercontent.com/assets/2133137/11108261/35d183d4-889a-11e5-9572-85e9d6cebd26.png">

Author: Andrew Or <02e0a999c50b1f88df7a8f5a04e1b76b35ea6a88@databricks.com>

Closes #9638 from andrewor14/fix-kryo-docs.

(cherry picked from commit cf38fc7551f4743958c2fdc7931affd672755e68)
Signed-off-by: Andrew Or <02e0a999c50b1f88df7a8f5a04e1b76b35ea6a88@databricks.com>

haowu80s/spark,haowu80s/spark,haowu80s/spark,haowu80s/spark,haowu80s/spark,haowu80s/spark