Remove explicit pinning of golang version 📌
Remove explicit pinning of golang version 📌

The nightly triggers unit tests were failing to build b/c they are now using
tests that require golang 1.14 features (specifically Cleanup) and the
version was explicitly pinned to 1.13. The tektoncd/pipeline release
pipelines do not explicitly pin the version and looking at the
golang-test task in the catalog the default version is "latest".
(https://github.com/tektoncd/catalog/blob/972bca5c5642a056c28ff1976c30c7367e6a9c3a/task/golang-test/0.1/golang-test.yaml#L23)
We could pin it to something explicit if we want; if so we should do it
for all of our pipelines. In the meantime removing the explicit pin so
we can use the default and the unit tests can pass.

Fixes #793

tektoncd/triggers,tektoncd/triggers