Set Oj default_option indent to 0 before #perform_items is run and reset after completed
Set Oj default_option indent to 0 before #perform_items is run and reset after completed

- Issue was brought up here: https://github.com/ankane/searchkick/issues/196
- During elasticsearch transport any Oj `indent` option other than 0
  will cause an error like what was reported

yardclub/searchkick,yardclub/searchkick