Set brew environment variables with `eval (brew shellenv)`

[simonrouse9461]

Setting up brew environment isn't just about setting the path. Homebrew has a command brew shellenv for configuring all the environment variables need to be set.

Here is what brew shellenv returns

set -gx HOMEBREW_PREFIX "/usr/local";
set -gx HOMEBREW_CELLAR "/usr/local/Cellar";
set -gx HOMEBREW_REPOSITORY "/usr/local/Homebrew";
set -g fish_user_paths "/usr/local/bin" "/usr/local/sbin" $fish_user_paths;
set -q MANPATH; or set MANPATH ''; set -gx MANPATH "/usr/local/share/man" $MANPATH;
set -q INFOPATH; or set INFOPATH ''; set -gx INFOPATH "/usr/local/share/info" $INFOPATH;

So for complete brew integration, eval ($HOMEBREW_BIN shellenv) need to be added to the beginning of the script, where $HOMEBREW_BIN has a default value of "/usr/local/bin/brew", but can be overridden by the user in "before.init.fish" in the omf configuration path.