Change InnerHits.fields from Fields to Field[] (#4312)

Author: flobernd

specification/_global/search/_types/hits.ts

@@ -127,7 +127,7 @@ export class InnerHits {
   ignore_unmapped?: boolean
   script_fields?: Dictionary<Field, ScriptField>
   seq_no_primary_term?: boolean
-  fields?: Fields
+  fields?: Field[]
   /**
    * How the inner hits should be sorted per `inner_hits`.
    * By default, inner hits are sorted by score.