clone arrays so we don't alter input values

Author: wvanderdeijl

Diff for: src/diff/array.js

@@ -2,7 +2,7 @@ import Diff from './base';
 
 export const arrayDiff = new Diff();
 arrayDiff.tokenize = arrayDiff.join = function(value) {
-  return value;
+  return value.slice();
 };
 
 export function diffArrays(oldArr, newArr, callback) { return arrayDiff.diff(oldArr, newArr, callback); }