change if else

tasks/mergefq.wdl

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