adopt ulimits on TravisCI to reflect important system settings
adopt ulimits on TravisCI to reflect important system settings

according to ES 5.0 upgrade it is necessary to increase the limits of
open file descriptors and adapt the number of threads.

https://www.elastic.co/guide/en/elasticsearch/reference/5.4/system-config.html

EvilMcJerkface/crate,crate/crate,EvilMcJerkface/crate,crate/crate,crate/crate,EvilMcJerkface/crate