Fix heading level of logging drivers

Syslog was a heading-2, but should be heading-3;
changed the headings to heading-4 to match the
"network settings" section.

Also changed "Log driver" to "logging driver" for JSON.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

docs/sources/reference/run.md

@@ -742,17 +742,17 @@ familiar with using LXC directly.
 
 You can specify a different logging driver for the container than for the daemon.
 
-### Logging driver: none
+#### Logging driver: none
 
 Disables any logging for the container. `docker logs` won't be available with
 this driver.
 
-### Log driver: json-file
+#### Logging driver: json-file
 
 Default logging driver for Docker. Writes JSON messages to file. `docker logs`
 command is available only for this logging driver
 
-## Logging driver: syslog
+#### Logging driver: syslog
 
 Syslog logging driver for Docker. Writes log messages to syslog. `docker logs`
 command is not available for this logging driver