`ast-types` and `react-docgen` should be (peer)Dependencies

[KaiVolland]

I'm using this package via react-stylegudist. But it seems that ast-types is not reachable from the index.js:

Error: Cannot find module 'ast-types/main'
Require stack:
- …/node_modules/react-docgen-annotation-resolver/index.js
- …/node_modules/react-styleguidist/lib/scripts/schemas/config.js
- …/node_modules/react-styleguidist/lib/scripts/config.js
- …/node_modules/react-styleguidist/lib/bin/styleguidist.js

As the index.js requires both ast-types and react-docgen these should be either dependencies or peerDepencies.