remove ? of tast value

tasks/mergefq.wdl

@@ -9,7 +9,7 @@ task mergefq {
 
 	command <<<
 		set -euo pipefail
-		if [ ! ${fq3} ]; then
+		if [  ${fq3} != "" ]; then
 		cat ${fq1} ${fq2} > ${fq_m}
 		else
 		cat ${fq1} ${fq2} ${fq3} > ${fq_m}