for loop simplify in array pair sum case

[yuanyan]

https://github.com/blakeembrey/code-problems/blob/master/array-pair-sum/array-pair-sum.js#L10

for (var i = 0; i < (hash[k - number] || 0); i++) {

can be simplified as

for (var i = 0; i <  hash[k - number]; i++) {