fix contentType definition for Solr html responswriter

from xml to html
(hint: value is currently not used, but is in SolrServlet)

source/net/yacy/cora/federate/solr/responsewriter/GrepHTMLResponseWriter.java

@@ -68,7 +68,7 @@ public class GrepHTMLResponseWriter implements QueryResponseWriter {
 
     @Override
     public String getContentType(final SolrQueryRequest request, final SolrQueryResponse response) {
-        return CONTENT_TYPE_XML_UTF8;
+        return "text/html";
     }
 
     @Override

source/net/yacy/cora/federate/solr/responsewriter/HTMLResponseWriter.java

@@ -60,7 +60,7 @@ public class HTMLResponseWriter implements QueryResponseWriter {
 
     @Override
     public String getContentType(final SolrQueryRequest request, final SolrQueryResponse response) {
-        return CONTENT_TYPE_XML_UTF8;
+        return "text/html";
     }
 
     @Override