The javac task doesn't explicitly state source and target version. Descriptor uses java 1.7; I didn't investigate the other dependencies.
Maybe add the source="${source-and-target-java-version}" and target="${source-and-target-java-version}" attributes to the ant task and set source-and-target-java-version to the version needed.
It works with Java 1.7 on my machine, so - without further investigating the other libraries - that should be fine. I changed build.xml as you suggested.
The javac task doesn't explicitly state source and target version. Descriptor uses java 1.7; I didn't investigate the other dependencies.
Maybe add the
source="${source-and-target-java-version}"
andtarget="${source-and-target-java-version}"
attributes to the ant task and setsource-and-target-java-version
to the version needed.