gffread: add -x and -M option

src/nf_modules/gffread/main.nf

@@ -25,6 +25,6 @@ process gffread {
     file_prefix = file_id
   }
   """
-  gffread ${gtf} -g ${fasta} -x -o ${file_prefix}.fasta
+  gffread ${gtf} -g ${fasta} -M -x ${file_prefix}.fasta
   """
-}
+}
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