mm-plugin install conflicts with existing package.json

[danfinlay]

Steps to reproduce:

• Start with your own package.json
• yarn add mm-plugin -D to install mm-plugin as a dev dependency
• run yarn mm-plugin init to run the mm-plugin

Problems:

• Notice all of the mm-plugin (dev dependencies) are flattened and added to dependencies
• Notice undefined is added as a prefix to all dependency versions.

Found by @whymarrh

[rekmarks]

This is due to mm-plugin using the init module of from the npm CLI. Working on a fix.

[rekmarks]

Fixed by 436b635