Restricting build matrix to the oldest and latest go versions we support.
Installing golint before checking out source to avoid accidental changes to the module dependencies (go.mod and go.sum files).
Bumped the go version to 1.16 for the GOPATH build, since in this mode go pulls all the dependencies at their HEAD versions, and some of them no longer works on go 1.12.
golintbefore checking out source to avoid accidental changes to the module dependencies (go.modandgo.sumfiles).