Flux 1.13.2

This is a patch release, including a fix for problems with using image
labels as timestamps.

Fixes

• Because image labels are inherited from base images, fluxd cannot indiscriminately use labels to determine the image created date. You must now explicitly allow that behaviour with the argument --registry-use-labels weaveworks/flux#2176
• Image timestamps can be missing (or zero) if ordering them by semver version rather than timestamp weaveworks/flux#2175
• Environment variables needed by the Google Cloud SDK helper are now propagated to git weaveworks/flux#2222

Maintenance and documentation

• Image builds are pushed to both weaveworks/ and fluxcd/ orgs on DockerHub, in preparation for the project moving organisations weaveworks/flux#2213
• Calculate Go dependencies more efficiently during the build weaveworks/flux#2207
• Refactor to remove a spurious top-level package weaveworks/flux#2201
• Update the version of Kubernetes-in-Docker used in end-to-end test, to v0.4.0 weaveworks/flux#2202
• Bump the Ubuntu version used in CI weaveworks/flux#2195

Thanks

Thanks go to the following for contributions: @2opremio, @4c74356b41, @ArchiFleKs, @adrian, @alanjcastonguay, @alexanderbuhler, @alexhumphreys, @bobbytables, @derrickburns, @dholbach, @dlespiau, @gaffneyd4, @hiddeco, @hkalsi, @hlascelles, @jaksonwkr, @jblunck, @jwenz723, @linuxbsdfreak, @luxas, @mpashka, @nlamot, @semyonslepov, @squaremo, @stefanprodan, @tegamckinney, @ysaakpr.