Try installing java7

Author: stsewd

scripts/travis/install_elasticsearch.sh

@@ -1,5 +1,6 @@
 if [ $ES_VERSION ]
 then
+    sudo apt-get install openjdk-7-jre
     sudo apt-get purge -y elasticsearch
     wget https://download.elastic.co/elasticsearch/elasticsearch/elasticsearch-${ES_VERSION}.tar.gz
     tar -xzf elasticsearch-${ES_VERSION}.tar.gz