Update Java documentation for 5.0

Fix after review

docs/java-api/aggregations/bucket/histogram-aggregation.asciidoc

@@ -36,7 +36,7 @@ Histogram agg = sr.getAggregations().get("agg");
 
 // For each entry
 for (Histogram.Bucket entry : agg.getBuckets()) {
-    Double key = (Double) entry.getKey();   // Key
+    Number key = (Number) entry.getKey();   // Key
     long docCount = entry.getDocCount();    // Doc count
 
     logger.info("key [{}], doc_count [{}]", key, docCount);