Gunzip: "error" logging level on inflate() errors.

Errors can easily happen due to broken upstream responses, there is no
need to log them at "alert" level.

src/http/modules/ngx_http_gunzip_filter_module.c

diff --git a/src/http/modules/ngx_http_gunzip_filter_module.c b/src/http/modules/ngx_http_gunzip_filter_module.c
index c2d504e..9a1ce41 100644
--- a/src/http/modules/ngx_http_gunzip_filter_module.c
+++ b/src/http/modules/ngx_http_gunzip_filter_module.c
@@ -422,7 +422,7 @@
     rc = inflate(&ctx->zstream, ctx->flush);
 
     if (rc != Z_OK && rc != Z_STREAM_END && rc != Z_BUF_ERROR) {
-        ngx_log_error(NGX_LOG_ALERT, r->connection->log, 0,
+        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                       "inflate() failed: %d, %d", ctx->flush, rc);
         return NGX_ERROR;
     }