Fix class name does not apply to checkbox field bug.

src/bootstrap-table.js

@@ -1583,8 +1583,8 @@
                     type = column.checkbox ? 'checkbox' : type;
                     type = column.radio ? 'radio' : type;
 
-                    text = [that.options.cardView ?
-                        '<div class="card-view">' : '<td class="bs-checkbox">',
+                    text = [sprintf(that.options.cardView ?
+                        '<div class="card-view %s">' : '<td class="bs-checkbox %s">', column['class'] || ''),
                         '<input' +
                         sprintf(' data-index="%s"', i) +
                         sprintf(' name="%s"', that.options.selectItemName) +