fix openapi

src/app.controller.ts

@@ -7,7 +7,7 @@ import {
   StreamableFile,
 } from '@nestjs/common';
 import { AppService } from './app.service';
-import { ApiOperation, ApiParam } from '@nestjs/swagger';
+import { ApiOperation, ApiParam, ApiProduces } from '@nestjs/swagger';
 import { BlankReturnMessageDto } from './dto/ReturnMessage.dto';
 
 @Controller()
@@ -21,6 +21,7 @@ export class AppController {
   @ApiParam({ name: 'username', description: '用户名' })
   @ApiParam({ name: 'size', description: '头像尺寸', type: 'number' })
   @ApiParam({ name: 'filename', description: '头像文件名' })
+  @ApiProduces('image/png')
   async getImage(
     @Param('username') username: string,
     @Param('size', ParseIntPipe) size: number,