Update install of uptimer for Golang 1.16

- make use of the uptimer_version variable
- go get doesn't clone the repo any more, so we can't run the unit tests

[#177373825](https://www.pivotaltracker.com/story/show/177373825)

dockerfiles/cf-deployment-concourse-tasks/Dockerfile

@@ -110,11 +110,9 @@ RUN \
  wget https://github.com/cloudfoundry/log-cache-cli/releases/download/v${log_cache_cli_version}/log-cache-cf-plugin-linux -P /tmp && \
  cf install-plugin /tmp/log-cache-cf-plugin-linux -f
 
-RUN go get -u github.com/cloudfoundry/uptimer && \
- go get -u github.com/onsi/ginkgo/... && \
- cd ${GOPATH}/src/github.com/cloudfoundry/uptimer && \
- ginkgo -r -randomizeSuites -randomizeAllSpecs && \
- cd -
+RUN \
+ go get -u github.com/cloudfoundry/uptimer@${uptimer_version} && \
+ go get -u github.com/onsi/ginkgo/...
 
 # Add trusted relint ca certificate
 ARG RELINT_CA_CERTIFICATE