changed regex for username detection

so usernames with - and _ and domains with - work

Signed-off-by: Jonas Sulzer <jonas@violoncello.ch>

src/components/Composer.vue

@@ -434,7 +434,7 @@ export default {
 				emoji.replaceWith(em)
 			})
 			let to = []
-			const re = /@((\w+)(@[\w.]+)?)/g
+			const re = /@(([\w-\_.]+)(@[\w-.]+)?)/g
 			let match = null
 			do {
 				match = re.exec(element.innerText)