Set base_type to array

Author: Bellangelo

registries/_format/sf-integer.md

@@ -4,7 +4,7 @@ issue:
 description: structured fields integer as defined in [RFC8941]
 source: https://www.rfc-editor.org/rfc/rfc8941#name-integers
 source_label: RFC 8941
-base_type: integer, number
+base_type: [integer, number]
 layout: default
 ---