Restore spanish empty string translation

As spanish translations are mantained directly by developers and mainly thourgh code
i decided to restore this translation deleted by Crowdin so i18n-tasks missing task
do not fail for this cause when running :es locale. This is happenning because original
translation in main locale :en is an empty string, so Crowdin is deleting this string from
all languages.

config/locales/es/general.yml

@@ -432,6 +432,7 @@ es:
         one: 1 voto
         other: "%{count} votos"
       supports_necessary: "%{number} apoyos necesarios"
+      reason_for_supports_necessary: ""
       total_percent: 100%
       archived: "Esta propuesta ha sido archivada y ya no puede recoger apoyos."
       successful: "Esta propuesta ha alcanzado los apoyos necesarios."