Slowest way to find base commit of repo on github

SlowestBaseCommitSearch.js

var apibase = 'https://api.github.com/repos/Homebrew/brew';

var auth = {
  username: '<CHANGEME>',
  apikey: '<CHANGEME>'  
};

auth.token = 'Basic ' + btoa(auth.username + ':' + auth.apikey);

var opts = {
  method: 'GET',
  headers: {'Authorization': auth.token}
};

var dbgPrint = (msg) => ( (value) => { console.log(msg + ': %o', value); return value;} )
var apiReq = (url)=>fetch(apibase + url, opts).then(function (response) { return response.json();})
var getFirstSha = () => apiReq('/commits').then(obj=>obj[0].sha);
var getParentSha = (childSha) => {
    return apiReq('/git/commits/' + childSha)
        .then(obj=>( obj.parents.length!==0 ? obj.parents[0].sha : {final:obj.sha} ) );
var finished = (obj) => { return typeof(obj) == "object" };

var cont = sha => {
    if(finished(sha)) dbgPrint('Complete')(sha); // base case
    else getParentSha(sha).then(dbgPrint('Next')).then(cont); // reursive call
};

getFirstSha()
.then(dbgPrint('GetFistSha'))
.then(cont);