bug#32789: Bash finds old version of guix after guix pull

[Alex Branham]

Hello,

After installing guixsd (0.15) on a VM and doing "guix pull", "guix --version"
gives 0.14-<stuff>.

I asked about this on IRC a few weeks ago and got a helpful answer. All
I needed to do to fix is was to run a simple bash command.
Unfortunately, I've forgotten what that was :-(

Reporting here since I didn't find anything in the issue tracker when I
looked.

Thanks,
Alex