Make helmfile respect signals send by kill command (not only Ctrl+C in terminal) (#750)

Fixes #746 

Signed-off-by: Dmitry Chepurovskiy <me@dm3ch.net>
Signed-off-by: yxxhero <aiopsclub@163.com>
Co-authored-by: yxxhero <aiopsclub@163.com>

pkg/tmpl/context_funcs.go

@@ -1,6 +1,7 @@
 package tmpl
 
 import (
+	"context"
 	"errors"
 	"fmt"
 	"io"
@@ -174,7 +175,7 @@ func (c *Context) EnvExec(envs map[string]interface{}, command string, args []in
 	g.Go(func() error {
 		// We use CombinedOutput to produce helpful error messages
 		// See https://github.com/roboll/helmfile/issues/1158
-		bs, err := helmexec.Output(cmd)
+		bs, err := helmexec.Output(context.Background(), cmd)
 		if err != nil {
 			return err
 		}