Make !pfp fall back to current user

src/main.rs

@@ -701,9 +701,9 @@ fn define(ctx: &mut Context, message: &Message, args: Args) -> CommandResult {
 
 #[command]
 fn pfp(ctx: &mut Context, message: &Message) -> CommandResult {
-    // Get username from first mention, otherwise use input text
+    // Get username from first mention, otherwise use current username
     let user = match message.mentions.len() {
-        0 => return Err(CommandError("Please specify a username!".to_string())),
+        0 => &message.author,
         _ => &message.mentions[0],
     };