Fix bug where homebrew replacement wouldn't work

[cjappl]

Check list

• [x] I have performed a self-review of my code
• [x] I have commented my code in hard-to-understand areas
• [x] I have made corresponding changes to the documentation

Description

In our homebrew formula, we were replacing this line in the installation:

 Replace this:             'set -x FORGIT "$FORGIT_INSTALL_DIR/bin/git-forgit"',
  with this     :             "set -x FORGIT \"#{opt_prefix}/bin/git-forgit\""

However, later in the fish script, we ignored that, just basing it directly off of the install dir:

alias git-forgit "$FORGIT_INSTALL_DIR/bin/git-forgit"

This makes sure that we always line up and don't have `fish: Unknown command: /opt/homebrew/share/conf.d/bin/git-forgit

• (line 1):` as in #377

Fixes #377

Type of change

• [x] Bug fix

Test environment

• Shell
  • [ ] bash
  • [ ] zsh
  • [x] fish
• OS
  • [ ] Linux
  • [x] Mac OS X
  • [ ] Windows
  • [ ] Others: