simplify cfg reading / merging

lib/login.js

@@ -1,9 +1,7 @@
-import { homedir } from 'os';
-import path from 'path';
-import fs from 'fs-promise';
+import chalk from 'chalk';
 import fetch from 'node-fetch';
+import * as cfg from './cfg';
 import { stringify as stringifyQuery } from 'querystring';
-import chalk from 'chalk';
 
 const URL = 'http://api-registration.now.sh';
 
@@ -77,13 +75,6 @@ async function register () {
 }
 
 export default async function () {
-  const file = path.resolve(homedir(), '.now.json');
   const loginData = await register();
-  let existing = null;
-  try {
-    existing = await fs.readFile(file, 'utf8');
-    existing = JSON.parse(existing);
-  } catch (err) {}
-  const config = Object.assign({}, existing, loginData);
-  return fs.writeFile(file, JSON.stringify(config));
+  cfg.merge(loginData);
 }