As noted in #182, the usage of a fork with `replace` directives is
forbidden by Go[0], and leads to consumers of the CLI failing to `go
install` the module:

    go: dmd.tanna.dev/cmd/dmd@latest (in dmd.tanna.dev@v0.42.0):
	    The go.mod file for the module providing named packages contains one or
	    more replace directives. It must not contain directives that would cause
	    it to be interpreted differently than if it were the main module.

To avoid this, we can make sure we adjust our fork to have a new branch
that contains a redefined `module` path.

Closes #182.

[0]: https://github.com/golang/go/issues/44840