Find all node_modules directories, not only nearest to root

Findup searches for the first `node_modules` directory in cwd and
it's ancestors, but what if our generators in `~/node_modules`,
and we calling generator in directory, that has `node_modules`?
Right - `yo` will think, that you have 0 generators.

Closes #440
Merge branch 'floatdrop-findup-all-issue-440'