Use the correct DOT language syntax for an ID with a leading digit (0mp).

It turns out that my username (0mp) is not a valid ID in the DOT language
because it starts with a digit. The easiest way to fix it is to put my
username in double quotes.

Reported by: pstef
Reviewed by: krion (mentor)
Approved by: krion (mentor)
Differential Revision: https://reviews.freebsd.org/D16372