Update GoalManager.coffee

Justification:

For a negative goal like saveThangs, let's say you have 5 thangs on the save list.  As things stand, if you don't have a HowMany defined, then the number of needed deaths to fail is 

numNeeded = _.size(stateThangs) - Math.min((goal.howMany ? 1), _.size stateThangs) + 1
numNeeded = 5 - Math.min(1, 5) + 1
numNeeded = 5

So you would only fail the goal if all 5 thangs you were supposed to save died.  This is contrary to the comment right above this line:

saveThangs: by default we would want to save all the Thangs, which means that we would want none of them to be "done"

Therefore, I think it should be Math.max rather than Math.min.

numNeeded = _.size(stateThangs) - Math.max((goal.howMany ? 1), _.size stateThangs) + 1
numNeeded = 5 - Math.max(1, 5) + 1
numNeeded = 1

So any of the Thangs on the save list dying is enough to fail the goal.

As a double check, what if the level designer designated a HowMany of 5?

numNeeded = _.size(stateThangs) - Math.max((goal.howMany ? 1), _.size stateThangs) + 1
numNeeded = 5 - Math.max(5, 5) + 1
numNeeded = 1

So this is consistent.