Fix maintaining last sort object when called without arguments.

dist/jquery.shuffle.js

@@ -1261,7 +1261,7 @@ Shuffle.prototype.sort = function( opts ) {
 
     this._layout( items );
 
-    this.lastSort = opts;
+    this.lastSort = sortOptions;
   }
 };
 

dist/jquery.shuffle.modernizr.js

@@ -1267,7 +1267,7 @@ Shuffle.prototype.sort = function( opts ) {
 
     this._layout( items );
 
-    this.lastSort = opts;
+    this.lastSort = sortOptions;
   }
 };
 

src/shuffle.js

@@ -1244,7 +1244,7 @@ Shuffle.prototype.sort = function( opts ) {
 
     this._layout( items );
 
-    this.lastSort = opts;
+    this.lastSort = sortOptions;
   }
 };