git: mandoc(1): Update to 1.9.19.

[Thomas Nikolajsen]

>>     mandoc(1): Update to 1.9.19.
>>
>>     For a full list of changes, see <http://mdocml.bsd.lv/ChangeLog.html>.
>>
>>     Thanks-to: Kristaps Dzonsons
>
>I really love the default output from this tool, but we're not using it
>anywhere.  Any ideas on a good place to try it?

I think it is a very nice tool, but it still have a few problems:
 - SYSOPSIS not indented (2nd line)
 - No extra space after sentence (e.g. `.')

 -thomas