Add "Standard ML of New Jersey" default installation path

The defaul root installation directory of the "Standard ML of New Jersey" is
/usr/local/smlnj, the `sml` command is found under the "bin" directory wich is
not automatically found by SublimeText.

Ref: http://www.smlnj.org/dist/working/110.75/NOTES/MACOSXINSTALL

The installer is recommend by the [Programming Languages course in Coursera](https://www.coursera.org/course/proglang) and the course forum has a lot of request for SML support in SublimeText.