Implicitly fetch dependencies with on `go build'.
`go mod download' fetches full modules which is a waste of
disk space (~500M). `go get -d' would be the better way to prefetch
dependencies in prepare(), however does not work for golangci-lint.
Upstream doesn't seem to care about this inconsistency. No point
in punishing users not having access to a fast internet connection
or have little disk space.