add string sample_id in ballgown task

tasks/ballgown.wdl

@@ -1,6 +1,7 @@
 task ballgown {
     File gene_abundance
     Array[File] ballgown
+    String sample_id
     String docker
     String cluster
     String disk_size

workflow.wdl

@@ -178,6 +178,7 @@ workflow {{ project_name }} {
 
 	call ballgown.ballgown as ballgown {
 		input: 
+		sample_id = sample_id,
 		docker = ballgown_docker,
 		cluster = ballgown_cluster,
 		ballgown = stringtie.ballgown,