Hello,

Excited to be submitting my first patch to guix!
The following patch updates elixir from 1.6.6 to 1.8.1.
This was almost a trivial patch, however the full path of the git 
executable
was causing a line to go over 80 chars, which caused a syntax check in 
the
elixir Makefile to fail. I added a quick workaround to use elixir's own 
syntax
checker to fix the affected file (by putting each argument to the fn on 
its own line)
before the test is run.

Best,

Robert