[ElasticSearch] Fix: wrong variable name.
[ElasticSearch] Fix: wrong variable name.

Fixes #1519.
vishesh92/redash,EverlyWell/redash,vishesh92/redash,alexanderlz/redash,44px/redash,denisov-vlad/redash,alexanderlz/redash,rockwotj/redash,imsally/redash,moritz9/redash,getredash/redash,imsally/redash,crowdworks/redash,useabode/redash,chriszs/redash,M32Media/redash,rockwotj/redash,M32Media/redash,hudl/redash,denisov-vlad/redash,M32Media/redash,amino-data/redash,imsally/redash,alexanderlz/redash,44px/redash,crowdworks/redash,M32Media/redash,denisov-vlad/redash,moritz9/redash,amino-data/redash,44px/redash,chriszs/redash,chriszs/redash,chriszs/redash,hudl/redash,hudl/redash,amino-data/redash,rockwotj/redash,44px/redash,useabode/redash,vishesh92/redash,EverlyWell/redash,hudl/redash,moritz9/redash,getredash/redash,crowdworks/redash,alexanderlz/redash,amino-data/redash,useabode/redash,denisov-vlad/redash,getredash/redash,EverlyWell/redash,vishesh92/redash,getredash/redash,denisov-vlad/redash,rockwotj/redash,moritz9/redash,imsally/redash,crowdworks/redash,getredash/redash,useabode/redash,EverlyWell/redash