Update to indicate version in status API header

Author: jackycute

app.js

@@ -234,7 +234,8 @@ app.get('/status', function (req, res, next) {
   realtime.getStatus(function (data) {
     res.set({
       'Cache-Control': 'private', // only cache by client
-      'X-Robots-Tag': 'noindex, nofollow' // prevent crawling
+      'X-Robots-Tag': 'noindex, nofollow', // prevent crawling
+      'HackMD-Version': config.version
     })
     res.send(data)
   })