Update Numenera.html

Edited the roll d20 Difficulty names prompts in coded lines 335-344  routine>Simple.  Simple>Standard. Standard>Demanding. Demanding>difficult.  to reflect an accurate listing of the core rules difficulty categories matched to those of Numenera (tm) core rules book, DIFFICULTY CHART, Bottom of page 15.
Merge pull request #348 from Felix-P/patch-1

Update Numenera.html