I have a computer with a dual boot ubuntu 14.04/windows8.1. Recently, my windows screwed up and I had to factory reset it. Everything was fine: my system downgrade to windows 8 and I still had the grub to choose what operating system I'd like to use.

But as soon as I went into windows, I updated it to 8.1: that made the system boot directly to windows. Thankfully it didn't mess up with my linux partitions as I could see on GParted.

Then I put my ubuntu live usb and ran Boot-Repair. The log can be seen on http://paste.ubuntu.com/9304059/

But that didn't change anything, it boots to windows directly yet.
At the end of the boot-repair setup, it shows:

Boot successfully repaired.

You can now reboot your computer. Please do not forget to make your
BIOS boot on sda1/EFI/ubuntu/shimx64.efi file!

If your computer reboots directly into Windows, try to change the boot
order in your BIOS. If your BIOS does not allow to change the boot
order, change the default boot entry of the Windows bootloader. For
example you can boot into Windows, then type the following command in
an admin command prompt: bcdedit /set {bootmgr} path
EFIubuntushimx64.efi

I ran Powershell with adm rights on windows and run the command it gave me, but it said command specifications were not valid.

How can I fix my boot?