Update to upstream release 1.7.18
Details:
- Bugfix release, see https://github.com/containous/traefik/releases/tag/v1.7.17 (That's no typo. There are no functional changes between 1.7.17 and 1.7.18 in the upstream code. The upstream code gets a patch level bump each time the released binary changes in some way, including - as in this case - if it is built with a different version of go.)