Explicitly set directory permissions on $NODENV_ROOT/versions

In environments where File resource defaults are locked down, the $NODENV_ROOT/versions directory may be locked down. This might cause issues when using `nodenv` globally versus per-user.

This change explicitly sets directory permissions that allow world read/execute.
Merge pull request #1 from jfryman/jfryman-patch-2

Explicitly set directory permissions on $NODENV_ROOT/versions
Merge pull request #26 from jfryman/master

Explicitly set directory permissions on $NODENV_ROOT/versions