Rework _.unfold for clarity and to avoid JSHint warning W093.
Rework _.unfold for clarity and to avoid JSHint warning W093.

W093 is 'Did you mean to return a conditional instead of an assignment?"

nfang/lodash-contrib,nfang/lodash-contrib,bruun/underscore-contrib,Leeds-eBooks/underscore-contrib,qhenkart/underscore-contrib,node4good/lodash-contrib,documentcloud/underscore-contrib,documentcloud/underscore-contrib,daejinseok/underscore-contrib,RandomSeeded/underscore-contrib,bruun/underscore-contrib,node4good/lodash-contrib,RandomSeeded/underscore-contrib,daejinseok/underscore-contrib,qhenkart/underscore-contrib,Leeds-eBooks/underscore-contrib