DocCommand: use regex wildcard

The current command as such produces no output on mac term or bash shell.
Using regex wildcard works fine on mac and linux.

Documentation/op-guide/maintenance.md

@@ -87,7 +87,7 @@ Removing excessive keyspace data and defragmenting the backend database will put
 
 ```sh
 # get current revision
-$ rev=$(ETCDCTL_API=3 etcdctl --endpoints=:2379 endpoint status --write-out="json" | egrep -o '"revision":[0-9]*' | egrep -o '[0-9]*')
+$ rev=$(ETCDCTL_API=3 etcdctl --endpoints=:2379 endpoint status --write-out="json" | egrep -o '"revision":[0-9]*' | egrep -o '[0-9].*')
 # compact away all old revisions
 $ ETCDCTL_API=3 etcdctl compact $rev
 compacted revision 1516