cleanup(shellx): do not directly depend on apex/log (#357)

internal/cmd/jafar/main_test.go

@@ -6,6 +6,7 @@ import (
 	"runtime"
 	"testing"
 
+	"github.com/apex/log"
 	"github.com/ooni/probe-cli/v3/internal/cmd/jafar/iptables"
 	"github.com/ooni/probe-cli/v3/internal/shellx"
 )
@@ -74,7 +75,7 @@ func TestMustx(t *testing.T) {
 			called   int
 			exitcode int
 		)
-		err := shellx.Run("curl", "-sf", "") // cause exitcode == 3
+		err := shellx.Run(log.Log, "curl", "-sf", "") // cause exitcode == 3
 		mustx(err, "", func(ec int) {
 			called++
 			exitcode = ec