handle dir

-- index.html --
<!DOCTYPE html>
<html>
<meta name="go-import" content="vcs-test.golang.org/go/invalid-version git https://vcs-test.golang.org/git/invalid-version">
-- unicode/index.html --
<!DOCTYPE html>
<html>
<meta name="go-import" content="vcs-test.golang.org/go/invalid-version git https://vcs-test.golang.org/git/invalid-version">
