lorri self-upgrade local fails

[codygman]

Describe the bug
While trying to see if test if issue #374 was fixed by recent changes, I followed these instructions to upgrade and lorri self-upgrade local failed.

To Reproduce
Steps to reproduce the behavior:

[cody@nixos:~/code/lorri]$ git log --oneline -n1
11693cf (HEAD -> master, origin/master, origin/HEAD) Merge pull request #441 from target/ops-direnv-check-varlink-errors

[cody@nixos:~/code/lorri]$ git status
On branch master
Your branch is up to date with 'origin/master'.

nothing to commit, working tree clean

[cody@nixos:~/code/lorri]$ lorri self-upgrade local .
Upgrading from source: .
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Exit { cmd: "\"nix-instantiate\" \"--eval\" \"--json\" \"--strict\" \"-A\" \"changelog\" \"--argstr\" \"src\" \".\" \"--\" \"/home/cody/.cache/lorri/cas/e168d15ac10f05da90ad4809d6bec898\"", status: Some(1), logs: [LogLine("fatal: couldn\'t find remote ref HEAD"), LogLine("fatal: the remote end hung up unexpectedly"), LogLine("error: program \'git\' failed with exit code 128"), LogLine("(use \'--show-trace\' to show detailed location information)")] }', src/libcore/result.rs:999:5
stack backtrace:
   0: std::sys_common::backtrace::print
   1: std::panicking::default_hook::{{closure}}
   2: std::panicking::default_hook
   3: std::panicking::rust_panic_with_hook
   4: std::panicking::continue_panic_fmt
   5: rust_begin_unwind
   6: core::panicking::panic_fmt
   7: core::result::unwrap_failed
   8: lorri::ops::upgrade::main
   9: lorri::main
  10: std::rt::lang_start::{{closure}}
  11: std::panicking::try::do_call
  12: __rust_maybe_catch_panic
  13: std::rt::lang_start_internal
  14: main
  15: __libc_start_main
  16: _start
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Expected behavior
lorri upgrades successfully

Metadata

[cody@nixos:~/code/lorri]$ lorri info
error: The following required arguments were not provided:
    --shell-file <nix_file>

USAGE:
    lorri info --shell-file <nix_file>

For more information try --help

[cody@nixos:~/code/lorri]$ lorri info --shell-file shell.nix 
lorri version: 1.1
GC roots exist, shell_gc_root: "/home/cody/.cache/lorri/gc_roots/6610c9247c3f7c7e4166e23d59bc71a5/gc_root/shell_gc_root"

$ uname -a
Linux nixos 5.4.46 #1-NixOS SMP Wed Jun 10 18:24:58 UTC 2020 x86_64 GNU/Linux

Additional context