refactor: simply repositories autodiscover

lib/config/index.js

-const githubApi = require('../platform/github');
-const gitlabApi = require('../platform/gitlab');
-const vstsApi = require('../platform/vsts');
-
 const definitions = require('./definitions');
 
 const defaultsParser = require('./defaults');
@@ -9,6 +5,7 @@ const fileParser = require('./file');
 const cliParser = require('./cli');
 const envParser = require('./env');
 
+const { getPlatformApi } = require('../platform');
 const { resolveConfigPresets } = require('./presets');
 
 exports.parseConfigs = parseConfigs;
@@ -73,25 +70,10 @@ async function parseConfigs(env, argv) {
 
   if (config.autodiscover) {
     // Autodiscover list of repositories
-    if (config.platform === 'github') {
-      logger.info('Autodiscovering GitHub repositories');
-      config.repositories = await githubApi.getRepos(
-        config.token,
-        config.endpoint
-      );
-    } else if (config.platform === 'gitlab') {
-      logger.info('Autodiscovering GitLab repositories');
-      config.repositories = await gitlabApi.getRepos(
+    config.repositories = await getPlatformApi(config.platform).getRepos(
       config.token,
       config.endpoint
     );
-    } else if (config.platform === 'vsts') {
-      logger.info('Autodiscovering vsts repositories');
-      config.repositories = await vstsApi.getRepos(
-        config.token,
-        config.endpoint
-      );
-    }
     if (!config.repositories || config.repositories.length === 0) {
       // Soft fail (no error thrown) if no accessible repositories
       logger.info(