Remove unused namespaces

src/Volo.Abp.AspNetCore.Mvc.UI.Bootstrap/TagHelpers/Form/AbpValidationAttributeTagHelper.cs

@@ -1,7 +1,4 @@
-using System.Collections.Generic;
-using Microsoft.AspNetCore.Mvc.Rendering;
-using Microsoft.AspNetCore.Mvc.ViewFeatures;
-using Microsoft.AspNetCore.Razor.TagHelpers;
+using Microsoft.AspNetCore.Razor.TagHelpers;
 using Volo.Abp.DependencyInjection;
 
 namespace Volo.Abp.AspNetCore.Mvc.UI.Bootstrap.TagHelpers.Form

src/Volo.Abp.AspNetCore.Mvc.UI.Bootstrap/TagHelpers/Form/AbpValidationAttributeTagHelperService.cs

@@ -1,4 +1,5 @@
 using Microsoft.AspNetCore.Razor.TagHelpers;
+using Volo.Abp.AspNetCore.Mvc.UI.Bootstrap.Microsoft.AspNetCore.Razor.TagHelpers;
 
 namespace Volo.Abp.AspNetCore.Mvc.UI.Bootstrap.TagHelpers.Form
 {
@@ -6,7 +7,7 @@ namespace Volo.Abp.AspNetCore.Mvc.UI.Bootstrap.TagHelpers.Form
     {
         public override void Process(TagHelperContext context, TagHelperOutput output)
         {
-            output.Attributes.Add("class","text-danger");
+            output.Attributes.AddClass("text-danger");
         }
     }
 }