Tweaked One Light Syntax theme

This is a minor tweak on the stock One Light Syntax theme. In particular,

• it is crudely reverted to (probably) version 1.5.0, which is compatible with Atom version ~1.12.9 shipped with Debian Jessy, and

• it slightly darkens the comments (which turn out too light to work with on one of my devices while being fine elsewhere).

You probably won't use or install this theme unless you are in the same position as I and basically like the One Light themes.

Also, apologies for not basing the theme on the appropriate branch of the copied stock repository. Hopefully changes are too trivial for anyone to care.