boot/grub2/readme.txt: typo

Signed-off-by: Julien Olivain <ju.o@free.fr>
(cherry picked from commit 3fbc4e583fa97be4c68eae2c378d598286c8ee66)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

boot/grub2/readme.txt

@@ -51,7 +51,7 @@ grub-bios-setup does but it works anyway.
 To test your BIOS image in Qemu
 -------------------------------
 
-qemu-system-{i386,x86-64} -hda disk.img
+qemu-system-{i386,x86_64} -hda disk.img
 
 Notes on using Grub2 for x86/x86_64 EFI-based platforms
 =======================================================
@@ -93,7 +93,7 @@ To test your i386/x86-64 EFI image in Qemu
 
    [0] https://github.com/retrage/edk2-nightly
 
-2. qemu-system-{i386,x86-64} -bios <path-to-OVMF.fd> -hda disk.img
+2. qemu-system-{i386,x86_64} -bios <path-to-OVMF.fd> -hda disk.img
 
 Notes on using Grub2 for ARM u-boot-based platforms
 ===================================================