Maaslin2 version upadate to 1.18.0 (#6317)

* maaslin2 version update to 1.16.0

* removing test cases with fixed_effect=NULL

* use of reference in test cases : maaslin2

* working residuals, zip output

* test cases updated

* Update tools/maaslin2/macros.xml

Co-authored-by: paulzierep <paul.zierep@googlemail.com>

* setting --core to 1

* maaslin2 version update to 1.18.0

---------

Co-authored-by: paulzierep <paul.zierep@googlemail.com>

tools/maaslin2/macros.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0"?>
 <macros>
-    <token name="@TOOL_VERSION@">1.16.0</token>
+    <token name="@TOOL_VERSION@">1.18.0</token>
     <token name="@VERSION_SUFFIX@">0</token>
     <token name="@PROFILE@">20.01</token>
     <xml name="edam_ontology">