Math script points to archaic service

[docrinehart]

Update math script command to use mathjs found at https://github.com/hubot-scripts/hubot-calculator

[bptillman]

@docrinehart if you want to take a look at this together at some point, let me know and we can pair on it.

[bptillman]

@docrinehart it looks like there is now a replacement for the math script that could be brought in instead: https://github.com/hubot-scripts/hubot-calculator

[docrinehart]

(nice)

[docrinehart]

Since I haven't actually found time to do this, I'm unassigning from myself so someone can pick it up if they so desire.