Fix CI testing badges

[josephburnett]

It seems that the CI testing badges in README.md have stopped working. Perhaps the jchester-knative pipeline is torn down or broken by the golang module restructuring we've done.

https://wings.pivotal.io/teams/jchester-knative/pipelines/skenario/jobs/test/

[jchesterpivotal]

X-ref #65. The "Wings" service I was using has been winding down for some time and I've been remiss in migrating to another one.

That said, and as much as I deeply love Concourse, may it would be easier to switch to Github Actions for the immediate future? There's only one Job in the pipeline, after all.