[DOCS] Fix typo in rollup groups docs (elastic#62269)

Author: AndyHunt66

docs/reference/rollup/understanding-groups.asciidoc

@@ -36,7 +36,7 @@ based on which groups are potentially useful to future queries.  For example, th
 --------------------------------------------------
 // NOTCONSOLE
 
-Allows `date_histogram`'s to be used on the `"timestamp"` field, `terms` aggregations to be used on the `"hostname"` and `"datacenter"`
+Allows `date_histogram`s to be used on the `"timestamp"` field, `terms` aggregations to be used on the `"hostname"` and `"datacenter"`
 fields, and `histograms` to be used on any of `"load"`, `"net_in"`, `"net_out"` fields.
 
 Importantly, these aggs/fields can be used in any combination.  This aggregation:
@@ -245,4 +245,4 @@ There was previously an issue with document counts on "overlapping" job configur
 If there were  two Rollup jobs saving to the same index, where one job is a "subset" of another job, it was possible that document counts
 could be incorrect for certain aggregation arrangements.
 
-This issue has also since been eliminated in 6.4.0.
+This issue has also since been eliminated in 6.4.0.