Fixed a regression that caused SyntaxErrors on IE 11

The changes made in #1334 incorrectly used an arrow function and as this isn't supported on IE 11 it causes a SyntaxError to be thrown when loading chai.

Author: lnewson

lib/chai/core/assertions.js

@@ -3178,7 +3178,7 @@ module.exports = function (chai, _) {
     } else {
       if (isDeep) {
         this.assert(
-          list.some(possibility => _.eql(expected, possibility))
+          list.some(function(possibility) { return _.eql(expected, possibility) })
           , 'expected #{this} to deeply equal one of #{exp}'
           , 'expected #{this} to deeply equal one of #{exp}'
           , list