remove "Content-Encoding: gzip" in 304 response
sent by ngx_http_gzip_static_module

src/http/modules/ngx_http_not_modified_filter_module.c

diff --git a/src/http/modules/ngx_http_not_modified_filter_module.c b/src/http/modules/ngx_http_not_modified_filter_module.c
index 5312b3a..7058157 100644
--- a/src/http/modules/ngx_http_not_modified_filter_module.c
+++ b/src/http/modules/ngx_http_not_modified_filter_module.c
@@ -88,6 +88,11 @@
     ngx_http_clear_content_length(r);
     ngx_http_clear_accept_ranges(r);
 
+    if (r->headers_out.content_encoding) {
+        r->headers_out.content_encoding->hash = 0;
+        r->headers_out.content_encoding = NULL;
+    }
+
     return ngx_http_next_header_filter(r);
 }