migrate to "export default"

also, set no-use-before-define in linter

src/janitor.js

@@ -3,14 +3,10 @@ import BoxError from './boxerror.js';
 import debugModule from 'debug';
 import Docker from 'dockerode';
 import safe from 'safetydance';
-import * as tokens from './tokens.js';
+import tokens from './tokens.js';
 
 const debug = debugModule('box:janitor');
 
-export {
-    cleanupTokens,
-    cleanupDockerVolumes
-};
 
 const gConnection = new Docker({ socketPath: '/var/run/docker.sock' });
 
@@ -56,3 +52,8 @@ async function cleanupDockerVolumes() {
 
     debug('Cleaned up docker volumes');
 }
+
+export default {
+    cleanupTokens,
+    cleanupDockerVolumes
+};