Add missing translation

config/locales/en.yml

@@ -239,6 +239,7 @@ en:
       merged: "That organisation has already been merged. Select a different organisation."
       scheme_duplicates_not_resolved: "You must resolve all duplicates or indicate that there are no duplicates"
     not_answered: "You must answer %{question}"
+    not_number: "%{field} must be a number."
     invalid_option: "Enter a valid value for %{question}"
     invalid_number: "Enter a number for %{question}"
     no_address_found: "We could not find this address. Check the address data in your CSV file is correct and complete, or select the correct address using the CORE site."