Empty repo causes crash

[kitplummer]

➜  ~ cd Code; git clone https://github.com/amorphid/artifactory-elixir
Cloning into 'artifactory-elixir'...
warning: You appear to have cloned an empty repository.
➜  Code cd artifactory-elixir
➜  artifactory-elixir git:(master) git log
fatal: your current branch 'master' does not have any commits yet

➜  lowendinsight-hex git:(hex_pm_api) ✗ mix lei.analyze https://github.com/amorphid/artifactory-elixir

10:54:14.584 [error] Task #PID<0.92.0> started from #PID<0.225.0> terminating
** (Git.Error) fatal: ambiguous argument 'HEAD': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'

    lib/git.ex:128: Git.result_or_fail/1
    lib/git_module.ex:52: GitModule.get_contributor_count/1
    lib/analyzer_module.ex:50: AnalyzerModule.analyze/2
    (elixir 1.10.2) lib/task/supervised.ex:90: Task.Supervised.invoke_mfa/2
    (elixir 1.10.2) lib/task/supervised.ex:35: Task.Supervised.reply/5
    (stdlib 3.11.2) proc_lib.erl:249: :proc_lib.init_p_do_apply/3
Function: &AnalyzerModule.analyze/2
    Args: ["https://github.com/amorphid/artifactory-elixir", "mix task"]
** (EXIT from #PID<0.92.0>) an exception was raised:
    ** (Git.Error) fatal: ambiguous argument 'HEAD': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'

        lib/git.ex:128: Git.result_or_fail/1
        lib/git_module.ex:52: GitModule.get_contributor_count/1
        lib/analyzer_module.ex:50: AnalyzerModule.analyze/2
        (elixir 1.10.2) lib/task/supervised.ex:90: Task.Supervised.invoke_mfa/2
        (elixir 1.10.2) lib/task/supervised.ex:35: Task.Supervised.reply/5
        (stdlib 3.11.2) proc_lib.erl:249: :proc_lib.init_p_do_apply/3