s/operations/operators
s/operations/operators

Couldn't figure out why it wasn't working until I [looked at the test](https://github.com/crcn/sift.js/blob/master/test/custom-test.js) and saw it's called operators.
kucukkanat/sift.js,johnwillyn/sift.js,rumkin/sift.js,crcn/sift.js,crcn/sift.js,stoeffel/sift.js,TomNeyland/sift.js