Valid invitation fix (#5858)

* Invitation expiration date changed to 7 days. Serializer updated to check for validity of invite.

* Minor tweak to valid method in the invitation serializer

* Fixed validity check for invitation

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Co-authored-by: Ahmad Farhat <ahmad.af.farhat@gmail.com>

app/serializers/invitation_serializer.rb

@@ -20,6 +20,6 @@ class InvitationSerializer < ApplicationSerializer
   attributes :id, :email, :updated_at, :valid
 
   def valid
-    object.updated_at < Invitation::INVITATION_VALIDITY_PERIOD.ago
+    object.updated_at > Invitation::INVITATION_VALIDITY_PERIOD.ago
   end
 end