override rx directory permissions in deletePath()

This fixes instantiation of pythonPackages.pytest that produces a
directory with less permissions during one of it's tests that leads to
a nix error like:

error: opening directory ‘/tmp/nix-build-python2.7-pytest-2.9.2.drv-0/pytest-of-user/pytest-0/testdir/test_cache_failure_warns0/.cache’: Permission denied

0 files changed, 0 insertions, 0 deletions