Fix challenge embeds not posting

src/commands/challenge.rs

@@ -169,6 +169,7 @@ pub async fn submit(ctx: Context<'_>, submission: serenity::Attachment) -> Resul
             let mut image_file = File::create(format!("{}/{}", submission_images_dir, file_name))?;
             image_file.write_all(&image)?;
             image_file.flush()?;
+            submitted_images.push(file_name);
         }
         submitter_data.insert(String::from("images"), images.into());
         submitter_data.insert(String::from("id"), author.id.as_u64().to_string().into());