Fix IMAGE_F_NON_BOOTABLE definition to match mcuboot

The correct flag for IMAGE_F_NON_BOOTABLE should be 0x10 instead of 0x02
according to the mcuboot files:
https://github.com/JuulLabs-OSS/mcuboot/blob/3c469bc698a9767859ed73cd0201c44161204d5c/boot/bootutil/include/bootutil/image.h#L46

Signed-off-by: Alvaro Prieto <source@alvaroprieto.com>
diff --git a/image/image.go b/image/image.go
index f5dd1bb..1530ea3 100644
--- a/image/image.go
+++ b/image/image.go
@@ -46,8 +46,8 @@
  */
 const (
 	IMAGE_F_PIC          = 0x00000001
-	IMAGE_F_NON_BOOTABLE = 0x00000002 /* non bootable image */
 	IMAGE_F_ENCRYPTED    = 0x00000004 /* encrypted image */
+	IMAGE_F_NON_BOOTABLE = 0x00000010 /* non bootable image */
 )
 
 /*