Allow urls to be used as images (#38)

* Allow urls ending to be used as images 

This will allow commands that use the image argument type to accept urls that end in PNG, JPG, or GIF

* Fix lint

* Fix lint properly

* Remove useless else/if

types/image.js

@@ -1,12 +1,13 @@
 const { ArgumentType } = require('discord.js-commando');
 const fileTypeRe = /\.(jpe?g|png|gif)$/i;
+const request = require('node-superfetch');
 
 module.exports = class ImageArgumentType extends ArgumentType {
 	constructor(client) {
 		super(client, 'image');
 	}
 
-	validate(value, msg, arg) {
+	async validate(value, msg, arg) {
 		const attachment = msg.attachments.first();
 		if (attachment) {
 			if (!attachment.height || !attachment.width) return false;
@@ -14,12 +15,21 @@ module.exports = class ImageArgumentType extends ArgumentType {
 			if (!fileTypeRe.test(attachment.name)) return 'Please only send PNG, JPG, or GIF format images.';
 			return true;
 		}
+		if (fileTypeRe.test(value.toLowerCase())) {
+			try {
+				await request.get(value);
+				return true;
+			} catch (err) {
+				return false;
+			}
+		}
 		return this.client.registry.types.get('user').validate(value, msg, arg);
 	}
 
 	async parse(value, msg, arg) {
 		const attachment = msg.attachments.first();
 		if (attachment) return attachment.url;
+		if (fileTypeRe.test(value.toLowerCase())) return value;
 		const user = await this.client.registry.types.get('user').parse(value, msg, arg);
 		return user.displayAvatarURL({ format: 'png', size: 512 });
 	}