chore: fallback to "localhost" when DB_HOST isn't specified

Author: php-coder

src/templates/app.js.ejs

@@ -6,7 +6,7 @@ app.set('x-powered-by', false)
 
 const pool = mysql.createPool({
     connectionLimit: 2,
-    host: process.env.DB_HOST,
+    host: process.env.DB_HOST || 'localhost',
     user: process.env.DB_USER,
     password: process.env.DB_PASSWORD,
     database: process.env.DB_NAME