Update bootstrap-table.js

Cancel previous xhr request to server.

src/bootstrap-table.js

@@ -1846,7 +1846,10 @@
         if (this.options.ajax) {
             calculateObjectValue(this, this.options.ajax, [request], null);
         } else {
-            $.ajax(request);
+            if(this._xhr){
+                this._xhr.abort();
+            }
+            this._xhr = $.ajax(request);
         }
     };