boolean isUpdated() {
            if (srcFile.lastModified() > lastModified) {
                // Update last modified as a side effect
                lastModified = srcFile.lastModified();
                return true;
            } else {
                return false;
            }
        }
@return destination file which is absolute (and withing AssemblyFiles.assemblyDirectory)
src/main/java/io/fabric8/maven/docker/assembly/AssemblyFiles.java