Update mkdirp to ^1.0.0

[webmaster128]

This time we are lucky to have a patch release of the old mkdirp 0.5 branch (#5, #6). But in the long run, we should update to mkdirp ^1.0.0 (CHANGELOG).

[viankakrisna]

Indeed. Thank you! I'll be happy to merge a PR with this change.