Initial build checks for types before creating them

[kahboom]

Getting the following error on yarn start:

Error saving the types index [Error: ENOENT: no such file or directory, open 'dist/@mf-typescript/__types_index.json'] {
  errno: -2,
  code: 'ENOENT',
  syscall: 'open',
  path: 'dist/@mf-typescript/__types_index.json'
}

To reproduce:

1. rm -rf dist
2. yarn start
3. The directory and file are created on that same build, but only after the check, so it fails

If I kill the process and restart it goes away. Of course, I could just check in this file, but I'd rather not have to check in the dist dir.

If it's relevant, I'm using dynamic imports.

[pavandv]

This issue is been addressed in the #6 PR along with other issues which causes when used with dynamic imports.