fix(): 'write after end' error.

Author: ovvn

.gitignore

@@ -1 +1,2 @@
 .DS_Store
+/.idea/

index.js

@@ -1,7 +1,12 @@
 module.exports = function() {
   return function (req, res, next) {
     if (req.path === '/healthcheck') {
-      return res.status(200).end();
+      if (res.headersSent) {
+        console.warn('Attempted end response after headers were sent');
+        return next();
+      } else {
+        return res.status(200).end();
+      }
     }
     next();
   }