update go mod

Merge pull request ContentSquare#78 from lalex/header_auth

Allow to auth with the X-ClickHouse-User header

Issue ContentSquare#43

Fix issue ContentSquare#42

link allowed_params instead of listing them

make golint happy

* support for enable_http_compression parameter

* support external_data processing

sort Accept-Encoding header for getting the same cache key for differ…

…ent browsers

support `http-01` challenge for `letsencrypt`

* fix issue with caching of gzipped requests

* fix issue with partially written response caches when client closed connection