add html mime type as utf-8

apollo-common/src/main/java/com/ctrip/framework/apollo/common/controller/WebMvcConfig.java

 package com.ctrip.framework.apollo.common.controller;
 
+import org.springframework.boot.context.embedded.ConfigurableEmbeddedServletContainer;
+import org.springframework.boot.context.embedded.EmbeddedServletContainerCustomizer;
+import org.springframework.boot.context.embedded.MimeMappings;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.data.domain.PageRequest;
 import org.springframework.data.web.PageableHandlerMethodArgumentResolver;
@@ -11,7 +14,7 @@ import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter
 import java.util.List;
 
 @Configuration
-public class WebMvcConfig extends WebMvcConfigurerAdapter {
+public class WebMvcConfig extends WebMvcConfigurerAdapter implements EmbeddedServletContainerCustomizer {
 
   @Override
   public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
@@ -28,4 +31,10 @@ public class WebMvcConfig extends WebMvcConfigurerAdapter {
     configurer.ignoreAcceptHeader(true).defaultContentType(MediaType.APPLICATION_JSON);
   }
 
+  @Override
+  public void customize(ConfigurableEmbeddedServletContainer container) {
+    MimeMappings mappings = new MimeMappings(MimeMappings.DEFAULT);
+    mappings.add("html", "text/html;charset=utf-8");
+    container.setMimeMappings(mappings );
+  }
 }