default connection string

mongoose.js

@@ -1,5 +1,6 @@
 const mongoose = require('mongoose');
 const enabled = require('debug').enabled;
+const url = process.env.TALK_MONGO_URL || 'mongodb://localhost/talk';
 
 // Use native promises
 mongoose.Promise = global.Promise;
@@ -9,7 +10,7 @@ if (enabled('talk:db')) {
 }
 
 try {
-  mongoose.connect(process.env.TALK_MONGO_URL, (err) => {
+  mongoose.connect(url, (err) => {
     if (err) throw err;
     console.log('Connected to MongoDB!');
   });