test against modern version of guava

Author: mikesamuel

scripts/build_for_travis.sh

@@ -13,5 +13,6 @@ if echo $TRAVIS_JDK_VERSION | egrep -q 'jdk[67]'; then
  exec mvn verify -Dmaven.javadoc.skip=true $COMMON_FLAGS
 else
  # Build the whole kit-n-kaboodle.
- exec mvn -f aggregate verify $COMMON_FLAGS
+ mvn -f aggregate/pom.xml source:jar javadoc:jar verify $COMMON_FLAGS \
+ && mvn -Dguava.version=27.0-jre -f aggregate/pom.xml clean source:jar javadoc:jar verify $COMMON_FLAGS
 fi