update elastic7 version used for e2e on travis (#3492)
update elastic7 version used for e2e on travis (#3492)


pavlovicnemanja/superdesk-client-core,superdesk/superdesk-client-core,petrjasek/superdesk-client-core,superdesk/superdesk-client-core,superdesk/superdesk-client-core,pavlovicnemanja/superdesk-client-core,petrjasek/superdesk-client-core,pavlovicnemanja/superdesk-client-core,petrjasek/superdesk-client-core,petrjasek/superdesk-client-core,superdesk/superdesk-client-core,pavlovicnemanja/superdesk-client-core,pavlovicnemanja/superdesk-client-core,petrjasek/superdesk-client-core,superdesk/superdesk-client-core