Ian/80 20

@nicolashery ready for review i worked one the items in this card https://trello.com/c/pw8nT1Bl/40-5-blip-80-20-fixes-to-interaction
The Math.ceil call should become Math.floor, and the -1 should go away. As written, the 0 element will only happen if Math.random() actually returns 0.0 -- which has probably never happened in the history of the universe. Math.random() is guaranteed never to return 1.0, so the right equation is Math.floor(Math.random() * ERR_GENERIC_LIST.length)