Fix name of `enabled_position_increments`

[Mpdreamz]

elastic/elasticsearch#22895

Renamed with bwc in 5.x but in master we need to rename this property and in 5.x deprecate it when we release 6.0

[Mpdreamz]

We already send enabled_position_increments which wont work in <5.3 but i think the best thing is to leave it as is and the fix being upgrading to elasticsearch 5.3 and over.