Fix resource leak in FileUtil

Fix resource leak in FileUtil

This made ModuleTests.testBuildModuleAndApplyAspectsFromAspectPath fail
because a file delete job for a module JAR failed after a previous
compile job had called FileUtil.isZipFile(File) in which the opened zip
file was never closed. A try with resources fixes that.

Maybe the corresponding test worked on Linux before, I did not try. I
just know that Linux is more forgiving about deleting open files while
on Windows they are being locked, which makes Windows the better system
to search for open file leaks.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>