Minor fixes on error handling

Co-authored-by: César Gallego <gallego.cesar@gmail.com>

internal/cmd/set.go

@@ -1,8 +1,8 @@
 package cmd
 
 import (
-	"fmt"
 	"io"
+	"log"
 	"os"
 	"strings"
 
@@ -32,8 +32,7 @@ var SetCmd = &cobra.Command{
 		}
 
 		if err := client.SetData(dataURL, handler, args[0], r); err != nil {
-			os.Stderr.WriteString(fmt.Sprintf("%v\n", err))
-			os.Exit(1)
+			log.Fatal(err)
 		}
 	},
 }