Per the [`go` command specification](https://golang.org/cmd/go/#hdr-Package_lists),
the `...` wildcard matches the empty string. This makes commands like
`go <action> . ./...` unnecessary: they should use `go <action> ./...`.

This also fixes a bug with the `gofa` shortcut, where it would emit an
error if called from a directory containing no go source files (but
having subdirectories that _did_ contain go files).