add install asciidoctor to travis
add install asciidoctor to travis

spring-cloud/spring-cloud-security,raoghuge/spring-cloud-security,jmnarloch/spring-cloud-security,spring-cloud/spring-cloud-security,jmnarloch/spring-cloud-security,spring-cloud/spring-cloud-security,jmnarloch/spring-cloud-security,raoghuge/spring-cloud-security,raoghuge/spring-cloud-security