Using template literals for mongodb error message (#298)

thx to @NyashaNziramasanga

Author: NyashaNziramasanga

src/app.ts

@@ -33,7 +33,7 @@ mongoose.Promise = bluebird;
 mongoose.connect(mongoUrl, { useNewUrlParser: true, useCreateIndex: true, useUnifiedTopology: true } ).then(
     () => { /** ready to use. The `mongoose.connect()` promise resolves to undefined. */ },
 ).catch(err => {
-    console.log("MongoDB connection error. Please make sure MongoDB is running. " + err);
+    console.log(`MongoDB connection error. Please make sure MongoDB is running. ${err}`);
     // process.exit();
 });