fix(discord): ensure first group in list is notified (jef#1788)

This fix ensures that the `series` of a `link` is found in
`notifyGroupSeries`. Before this fix, the first key in
`notifyGroupSeries` was excluded.

src/notification/discord.ts

@@ -52,7 +52,7 @@ export function sendDiscordMessage(link: Link, store: Store) {
           notifyText = notifyText.concat(notifyGroup);
         }
 
-        if (Object.keys(notifyGroupSeries).indexOf(link.series) !== 0) {
+        if (Object.keys(notifyGroupSeries).indexOf(link.series) !== -1) {
           notifyText = notifyText.concat(notifyGroupSeries[link.series]);
         }