Fix RFC3339 typo in docs

Author: IJMacD

docs/reference/commandline/system_prune.md

@@ -107,7 +107,7 @@ The `until` filter can be Unix timestamps, date formatted
 timestamps, or Go duration strings (e.g. `10m`, `1h30m`) computed
 relative to the daemon machine’s time. Supported formats for date
 formatted time stamps include RFC3339Nano, RFC3339, `2006-01-02T15:04:05`,
-`2006-01-02T15:04:05.999999999`, `2006-01-02Z07:00`, and `2006-01-02`. The local
+`2006-01-02T15:04:05.999999999`, `2006-01-02T07:00`, and `2006-01-02`. The local
 timezone on the daemon will be used if you do not provide either a `Z` or a
 `+-00:00` timezone offset at the end of the timestamp.  When providing Unix
 timestamps enter seconds[.nanoseconds], where seconds is the number of seconds