lfe: fix install phase, make sure we get the binaries in the right place (#509423)

    beamDeps = [ proper ];

    makeFlags = [

      "-e"

      "MANDB=''"

      "PREFIX=$$out"

    ];

    # override buildRebar3's install to let the builder use make install

    installPhase = "";

    installPhase = ''

      runHook preInstall

      make -e MANDB= PREFIX=$out install

      runHook postInstall

    '';

    doCheck = true;

    checkTarget = "travis";

    doInstallCheck = true;

    installCheckPhase = ''

      runHook preInstallCheck

      test -e $out/bin/lfe

      runHook postInstallCheck

    '';

    postFixup = ''

      # LFE binaries are shell scripts which run erl and lfe.

      # Add some stuff to PATH so the scripts can run without problems.