[Doc] doc updates for date histogram interval

Close #5308

docs/reference/search/aggregations/bucket/datehistogram-aggregation.asciidoc

@@ -40,7 +40,7 @@ fractional values are allowed, for example 1.5 hours:
 }
 --------------------------------------------------
 
-Other available expressions for interval: `year`, `quarter`, `week`, `day`, `hour`, `minute`, `second`
+Available expressions for interval: `year`, `quarter`, `month`, `week`, `day`, `hour`, `minute`, `second`
 
 ==== Time Zone
 

docs/reference/search/facets/date-histogram-facet.asciidoc

@@ -27,7 +27,7 @@ facet>>. Here is a quick example:
 
 The `interval` allows to set the interval at which buckets will be
 created for each hit. It allows for the constant values of `year`,
-`quarter`, `month`, `week`, `day`, `hour`, `minute`.
+`quarter`, `month`, `week`, `day`, `hour`, `minute` ,`second`.
 
 It also support time setting like `1.5h` (up to `w` for weeks).