Fix include type in Significant Text Agg (#2279) (#2292)

Author: pquentin

output/schema/schema.json

@@ -334,7 +334,7 @@ export class SignificantTextAggregation extends BucketAggregationBase {
   field?: Field
   filter_duplicate_text?: boolean
   gnd?: GoogleNormalizedDistanceHeuristic
-  include?: string | string[]
+  include?: TermsInclude
   min_doc_count?: long
   mutual_information?: MutualInformationHeuristic
   percentage?: PercentageScoreHeuristic