[fit] add text/* mimetype for text serializer (#287)

Author: CodeCasterX

framework/fit/java/fit-builtin/services/fit-http-classic/definition/src/main/java/modelengine/fit/http/support/DefaultSerializers.java

@@ -10,7 +10,9 @@
 import static modelengine.fit.http.protocol.MimeType.APPLICATION_X_WWW_FORM_URLENCODED;
 import static modelengine.fit.http.protocol.MimeType.MULTIPART_FORM_DATA;
 import static modelengine.fit.http.protocol.MimeType.MULTIPART_MIXED;
+import static modelengine.fit.http.protocol.MimeType.TEXT_CSS;
 import static modelengine.fit.http.protocol.MimeType.TEXT_EVENT_STREAM;
+import static modelengine.fit.http.protocol.MimeType.TEXT_HTML;
 import static modelengine.fit.http.protocol.MimeType.TEXT_PLAIN;
 
 import modelengine.fit.http.Serializers;
@@ -74,6 +76,8 @@ private Map<MimeType, EntitySerializer<?>> loadEntitySerializers() {
                 .put(MULTIPART_FORM_DATA, EntitySerializer.multiPartSerializer())
                 .put(MULTIPART_MIXED, EntitySerializer.multiPartSerializer())
                 .put(TEXT_PLAIN, EntitySerializer.textSerializer())
+                .put(TEXT_CSS, EntitySerializer.textSerializer())
+                .put(TEXT_HTML, EntitySerializer.textSerializer())
                 .build();
         this.json().ifPresent(serializer -> {
             curSerializers.put(APPLICATION_JSON, EntitySerializer.jsonSerializer(serializer));