fix typo in Min bucket aggregation docs

docs/reference/search/aggregations/reducer/min-bucket-aggregation.asciidoc

@@ -1,5 +1,5 @@
 [[search-aggregations-reducer-min-bucket-aggregation]]
-=== Max Bucket Aggregation
+=== Min Bucket Aggregation
 
 A sibling reducer aggregation which identifies the bucket(s) with the minimum value of a specified metric in a sibling aggregation 
 and outputs both the value and the key(s) of the bucket(s). The specified metric must be numeric and the sibling aggregation must