Added error handler

Author: Dan Wahlin

src/lib/database.js

@@ -8,7 +8,12 @@ let   connection = null;
 class Database {
 
     open(callback) {
-        mongoose.connect(connectionString);
+        const options = {};
+        mongoose.connect(connectionString, options, (err) => {
+            if (err) {
+                console.log('mongoose.connect() failed: ' + err);
+            }
+        });
         connection = mongoose.connection;
         mongoose.Promise = global.Promise;