Simplify implicit snippy dependencies.

biocontainer tar doesn't support tar -z

tools/snippy/snippy.xml

@@ -54,7 +54,7 @@
         #end if
 
         mkdir -p ${dir_name} && cp -r out/reference out/snps.tab out/snps.aligned.fa out/snps.vcf ${dir_name}/ &&
-        tar -czf out.tgz ${dir_name}
+        tar -cf - ${dir_name} | gzip > out.tgz
         #if "outcon" in str($outputs) and $adv.rename_cons
           && sed -i 's/>.*/>${dir_name}/' out/snps.consensus.fa
         #end if