index output fix

tasks/indexBam.wdl

 task indexBam {
 	File sorted_bam
 	String sample
+	String base = basename(sorted_bam,'.bam')
+	String bam_index = base + ".bam.bai"
 	String SAMdocker
 	String cluster_config
 	String disk_size
     	dataDisk: "cloud_ssd " + disk_size + " /cromwell_root/"
 	}
 	output {
-		File sorted_bam_index = "${sample}.bam.bai"
+		File sorted_bam_index = bam_index
 	}
 }