Update node-build to origin branch correctly

[harryzcy]

Currently, asdf cmd nodejs update-nodebuild is broken.
It only git checkout the local branch, but never updates to the origin branch correctly. We should fast-forward after fetch and checkout.

[Stratus3D]

@augustobmoura can you review this one? I don't know that this change is needed.

[augustobmoura]

That's a good catch @harryzcy!
I changed some code around to fix another problem and forgot to add the merge command

Thank you for the contribution!