Set vm.max_map_count to 262144

scripts/travis/install_elasticsearch5.sh

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+sudo sysctl -w vm.max_map_count=262144
+
 sudo apt-get autoremove --purge elasticsearch
 wget -qO - https://artifacts.elastic.co/GPG-KEY-elasticsearch | sudo apt-key add -
 echo "deb https://artifacts.elastic.co/packages/5.x/apt stable main" | sudo tee -a /etc/apt/sources.list.d/elastic-5.x.list