Reduce memory for tests to 1792MB
Reduce memory for tests to 1792MB

Tested this on my laptop by running it at 1536MB several dozen times and
saw no failures. This should help Travis fail less

bd-dev-mobileum/presto,bd-dev-mobileum/presto,bd-dev-mobileum/presto,bd-dev-mobileum/presto,bd-dev-mobileum/presto