Inconsistent Use of Vendoring

[Adam Hughes]

This module includes a checked-in vendor/ directory, and portions of the Makefile appear to aim to help maintain it. For example, make dep runs go mod vendor, among other things.

On the other hand, the build target explicitly enables module mode via GO111MODULE=on, which if I'm reading this post correctly, means the vendor directory is ignored (assuming Go >= 1.11.) The test and cover don't explicitly set GO111MODULE, and so the behaviour of these rules depends on whether the code is being compiled inside or outside of $GOPATH/src.

Is there a compelling reason that vendor/ is required? The Go maintainers appear to be signalling a move away from vendoring going forward (ref), and removing it would make the repo smaller and the Makefile simpler.