email text adapted, hostname created from config file

config/config.js

 module.exports = {
   development: {
     app: {
+      hostname: 'm4lab.hft-stuttgart.de',
       name: 'User Account Management',
       port: process.env.PORT || 9989
     },

routes/routes.js

@@ -314,7 +314,7 @@ module.exports = function (app, config, passport) {
             emailSubject = "M4_LAB Password Reset";
             emailContent = "Hi User,\n\n"+
               "we've received a request to reset your password. If you didn't make the request, just ignore this email.\n\n"+
-              "Otherwise, you can reset your password using this link: http://" + req.headers.host + "/reset/" + token + "\n" +
+              "Otherwise, you can reset your password using this link: https://" + config.app.hostname + "/reset/" + token + "\n" +
               "This password reset is only valid for 1 hour.\n\n"+
               "Thanks,\nM4_LAB Team"