Check if path contains slashes after stripping
Check if path contains slashes after stripping

If we do `cabal2nix test/`, we need to add a `./` prefix because the
path doesn't contain any slashes after stripping.

psibi/cabal2nix,dmalikov/cabal2nix,gridaphobe/cabal2nix,spencerjanssen/cabal2nix,jb55/cabal2nix,bennofs/cabal2nix,Fuuzetsu/cabal2nix