title: Issues with swagger after migrating to .NET Core 3.0
body: <p>After migrating to .NET Core 3.0. I'm having issues configuring swagger. </p>
  
  <p>Following is my configuration.</p>
  
  <pre><code>  public void ConfigureServices(IServiceCollection services)
    {       
  
         services.AddMvc().SetCompatibilityVersion(Microsoft.AspNetCore.Mvc.CompatibilityVersion.Version_3_0).AddNewtonsoftJson();
  
  
         services.AddSwaggerGen(setup =&gt;
         {
               setup.SwaggerDoc(
                  "v1", 
                   new Info 
                   {  
                       Title = "Docker", 
                       Version = "v1" 
                   });
          });
    }
  
  public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
  {
         Configuration.SwaggerOptions swaggerOptions = new Configuration.SwaggerOptions();
  
         _configuration.GetSection("SwaggerOptions").Bind(swaggerOptions);
  
         app.UseSwagger(options =&gt;
         {
              options.RouteTemplate = swaggerOptions.JsonRoot;
         });
  
         app.UseSwaggerUI(options =&gt;
         {
             options.SwaggerEndpoint(swaggerOptions.UiEndpoint, swaggerOptions.ApiDescription);
         });
  }
  </code></pre>
  
  <p>Following is the exception </p>
  
  <blockquote>
    <p>TypeLoadException: Could not load type
    'Microsoft.AspNetCore.Mvc.MvcJsonOptions' from assembly
    'Microsoft.AspNetCore.Mvc.Formatters.Json</p>
  </blockquote>
  
  <p>Is there a solution for this ? </p>