Cache JDK8 installer on Travis

.travis.yml

   webhooks:
     - secure: "CrwnSt40WNegJOkgDOaCwUwP9fCgx68pYQWtcZnj4+bRF7kFuFI+EUFuf7G29oPOf9CjmFVvZ+mS/ZJ9AqtjfWh/Q9f4Zsv9BBfOmTgUcidYp8+hQljeesEXwi2Mqfa2JeRysje4xu2p8b52h+apbbQ2Y2FQsP4uwmj1LEpP32U="
   on_start: always
-
-addons:
-  apt:
-    packages:
-      # upgrade java 8 as the default version 1.8.0_31 prevents from compile sources
-      # https://github.com/travis-ci/travis-ci/issues/4042
-      - oracle-java8-installer

travis.sh

 
 function configureTravis {
   mkdir ~/.local
-  curl -sSL https://github.com/SonarSource/travis-utils/tarball/v25 | tar zx --strip-components 1 -C ~/.local
+  curl -sSL https://github.com/SonarSource/travis-utils/tarball/v29 | tar zx --strip-components 1 -C ~/.local
   source ~/.local/bin/install
   echo "$ARTIFACTORY_URL/npmjs/" > .npmrc
 }
 configureTravis
+. installJDK8
 
 function strongEcho {
   echo ""