Fix README.md minor error (#2620)

Example was re-using the moved `framework` value.

README.md

@@ -48,7 +48,7 @@ use serenity::async_trait;
 use serenity::prelude::*;
 use serenity::model::channel::Message;
 use serenity::framework::standard::macros::{command, group};
-use serenity::framework::standard::{StandardFramework, CommandResult};
+use serenity::framework::standard::{StandardFramework, Configuration, CommandResult};
 
 #[group]
 #[commands(ping)]
@@ -62,7 +62,7 @@ impl EventHandler for Handler {}
 #[tokio::main]
 async fn main() {
     let framework = StandardFramework::new().group(&GENERAL_GROUP);
-    framework.configure(|c| c.prefix("~")); // set the bot's prefix to "~"
+    framework.configure(Configuration::new().prefix("~")); // set the bot's prefix to "~"
 
     // Login with a bot token from the environment
     let token = env::var("DISCORD_TOKEN").expect("token");