easyui datagrid 列的内容超出所定义的列宽时,自动换行

<table id="_main_table"> 
   <thead> 
    <tr> 
     <th data-options="field:‘id‘,width:20">id</th>  
     <th data-options="field:‘doctorName‘,width:40,align:‘center‘">医生</th> 
     <th data-options="field:‘roleName‘,width:100,align:‘center‘">医生角色</th>     
     <th data-options="field:‘img‘,align:‘center‘,width:50,formatter:_opformatter2">操作</th> 
    </tr> 
   </thead> 
  </table> 

    $(‘#_main_table‘).datagrid({
                        method:‘get‘,
                         url: ‘xxxxx‘,
                         checkbox:true,
                         pagination: true,
                         fit: true,
                         cache:false, 
                         fitColumns: true,
                         border: false,
                         rownumbers: true,
                         nowrap:false,                     
                         frozenColumns:[[
                                        {field:‘id‘,checkbox:true,hidden:true}
                                    ]],        
                         loadFilter: function(data) { return data.data;
                         },
                        });