修复/api/UEditor请求，返回的中文乱码

[amusement1234]

UEditorNetCore/src/UEditorNetCore/Handlers/Handler.cs

Line 29 in ba4ed5a

Response.Headers.Add("Content-Type", "text/plain");

改为：Response.Headers.Add("Content-Type", "text/plain;charset=utf-8");