add 'channels:join' scope

packages/slack/src/utils/required-scopes.ts

@@ -1 +1,10 @@
-export const requiredScopes: string[] = ['commands', 'team:read', 'chat:write', 'channels:history', 'groups:history', 'im:history', 'mpim:history'];
+export const requiredScopes: string[] = [
+  'commands',
+  'team:read',
+  'chat:write',
+  'channels:join',
+  'channels:history',
+  'groups:history',
+  'im:history',
+  'mpim:history',
+];