[SPARK-2976] Replace tabs with spaces

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #1895 from sarutak/SPARK-2976 and squashes the following commits:

1cf7e69 [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-2976
d1e0666 [Kousuke Saruta] Modified styles
c5e80a4 [Kousuke Saruta] Remove tab from JavaPageRank.java and JavaKinesisWordCountASL.java
c003b36 [Kousuke Saruta] Removed tab from sorttable.js