Merge pull request #2294 from dexie/liz/fix-sortby-immutable-cache

fix: Collection.sortBy() throws on frozen arrays in immutable cache mode

Author: dfahlander

src/classes/collection/collection.ts

@@ -195,7 +195,7 @@ export class Collection implements ICollection {
       return cmp(aVal, bVal) * order;
     }
     return this.toArray(function (a) {
-      return a.sort(sorter);
+      return a.slice().sort(sorter);
     }).then(cb);
   }