Quick fix

`undefined method `<' for nil`

https://appsignal.com/csa-admin/sites/672e0b61d2a5e4b5197f10e4

```
app/models/member.rb:292 activate!
app/models/member.rb:271 review_active_state!
lib/active_support/callbacks.rb:361 block in make_lambda
lib/active_support/callbacks.rb:207 call
lib/active_support/callbacks.rb:562 block in invoke_after
lib/active_support/callbacks.rb:562 each
lib/active_support/callbacks.rb:562 invoke_after
lib/active_support/callbacks.rb:110 run_callbacks
lib/active_support/callbacks.rb:912 _run_update_callbacks
lib/active_record/callbacks.rb:449 _update_record
lib/active_record/timestamp.rb:122 _update_record
lib/active_record/persistence.rb:894 create_or_update
lib/active_record/callbacks.rb:441 block in create_or_update
lib/active_support/callbacks.rb:120 block in run_callbacks
lib/active_record/autosave_association.rb:396 around_save_collection_association
lib/active_support/callbacks.rb:129 block in run_callbacks
lib/active_support/callbacks.rb:140 run_callbacks
lib/active_support/callbacks.rb:912 _run_save_callbacks
lib/active_record/callbacks.rb:441 create_or_update
lib/active_record/timestamp.rb:127 create_or_update
lib/active_record/persistence.rb:424 save!
lib/active_record/validations.rb:54 save!
lib/active_record/transactions.rb:366 block in save!
```

app/models/member.rb

@@ -289,7 +289,7 @@ def activate!
     self.activated_at = Time.current
     save!
 
-    if emails? && activated_at_previously_was.nil? || activated_at_previously_was < 1.week.ago
+    if emails? && (activated_at_previously_was.nil? || activated_at_previously_was < 1.week.ago)
       MailTemplate.deliver_later(:member_activated, member: self)
     end
   end