change status code and add log message

src/http/modules/ngx_http_dav_module.c

diff --git a/src/http/modules/ngx_http_dav_module.c b/src/http/modules/ngx_http_dav_module.c
index bfb12db..8c45e64 100644
--- a/src/http/modules/ngx_http_dav_module.c
+++ b/src/http/modules/ngx_http_dav_module.c
@@ -153,7 +153,9 @@
     case NGX_HTTP_PUT:
 
         if (r->uri.data[r->uri.len - 1] == '/') {
-            return NGX_HTTP_BAD_REQUEST;
+            ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
+                          "can not PUT to a collection");
+            return NGX_HTTP_CONFLICT;
         }
 
         r->request_body_in_file_only = 1;