[Docs] Correct spark.files.fetchTimeout default value

change the value of spark.files.fetchTimeout

Author: viper-kun <xukun.xu@huawei.com>

Closes #2406 from viper-kun/master and squashes the following commits:

ecb0d46 [viper-kun] [Docs] Correct spark.files.fetchTimeout default value
7cf4c7a [viper-kun] Update configuration.md