Migrate to Go modules and remove vendor dir

[carlosedp]

Expected Behaviour

Use Go modules instead of dep and remove vendor directory since go modules now handles caching into ~/go/pkg/mod.

The advantage is that it's built-in Go since 1.13 and production on 1.14 ready as stated in https://blog.golang.org/go1.14.

Current Behaviour

Building requires dep, an external application.

Possible Solution

Will submit a PR if the proposal gets +1.

[alexellis]

Not approved. Please hold off on this.

[alexellis]

We've gone over to Go modules, but the vendor directory should say.