update mergekmer.nf output to match input of kmerclust

src/modules/mergekmer.nf

@@ -35,7 +35,7 @@ process COLLATEKMER {
     tuple val(specie), path(csv)
 
     output:
-    path("*.csv"), emit: csv
+    tuple val(species), path("*.csv"), emit: csv
     path "versions.yml", emit: versions
 
     script: