Remove need for fake `go.mod`

[bwplotka]

Unfortunately as per Go 1.14 --moddir feature: https://golang.org/doc/go1.14#go-flags:

A file named go.mod must still be present in order to determine the module root directory, but it is not accessed.

This means that we need to maintain in .bingo dir a fake empty go.mod. Let's create some issue on upstream why this is needed in Go itself and if we can remove that need.