Added dppx value for HTC One

Chrome in the HTC one reports height/width of 640/360, which is 1/3 of
the DPI of 1920/1080, so I assume means a dppx of 3.
Opting out of Jekyll for my fork of this project

I don't need to build it...
Merge pull request #39 from alastc/gh-pages

Added dppx value for HTC One