fix Taskvars.yml vars not available while interpolating vars prop

closes #40

task.go

@@ -98,7 +98,7 @@ func (e *Executor) Run(args ...string) error {
 	}
 
 	for _, a := range args {
-		if err := e.RunTask(context.Background(), Call{Task: a}); err != nil {
+		if err := e.RunTask(context.Background(), Call{Task: a, Vars: e.taskvars}); err != nil {
 			return err
 		}
 	}

task_test.go

@@ -236,6 +236,7 @@ func TestParams(t *testing.T) {
 		{"dep2.txt", "Dependence2\n"},
 		{"spanish.txt", "¡Holla mundo!\n"},
 		{"spanish-dep.txt", "¡Holla dependencia!\n"},
+		{"portuguese.txt", "Olá, mundo!\n"},
 	}
 
 	for _, f := range files {

testdata/params/Taskfile.yml

@@ -1,6 +1,7 @@
 default:
   vars:
     SPANISH: ¡Holla mundo!
+    PORTUGUESE: "{{.PORTUGUESE}}"
   deps:
     - task: write-file
       vars: {CONTENT: Dependence1, FILE: dep1.txt}
@@ -17,6 +18,8 @@ default:
       vars: {CONTENT: "!", FILE: exclamation.txt}
     - task: write-file
       vars: {CONTENT: "{{.SPANISH}}", FILE: spanish.txt}
+    - task: write-file
+      vars: {CONTENT: "{{.PORTUGUESE}}", FILE: portuguese.txt}
 
 write-file:
   cmds:

testdata/params/Taskvars.yml

@@ -0,0 +1 @@
+PORTUGUESE: Olá, mundo!