FIX: emoji autocomplete not triggering correctly

08044b4f regressed emoji auto complete logic since we (I) forgot to add the
space into the not capturing group at the beginning.

This meant that

`hello 👍t` would not trigger an autocomplete to pick skin tone.

app/assets/javascripts/discourse/app/components/d-editor.js

@@ -440,7 +440,7 @@ export default Component.extend({
           return false;
         }
 
-        const matches = /(?:^|[>.,\/#!$%^&*;:{}=\-_`~()])(:(?!:).?[\w-]*:?(?!:)(?:t\d?)?:?) ?$/gi.exec(
+        const matches = /(?:^|[\s.\?,@\/#!%&*;:\[\]{}=\-_()])(:(?!:).?[\w-]*:?(?!:)(?:t\d?)?:?) ?$/gi.exec(
           text.substring(0, cp)
         );