fix(monorepo): fix babel options resolve

[karolis-sh]

fix #102

I think I fixed the monorepo cases just the way they worked in babel 6.

EDIT: Though now that I think about it I'm not sure if this is the desired approach. This fixes the breaking change (for some users), but previous lookup by package.json seems more predictable as usually you babelify from child package not the root one. And there's the cwd option how that should work in monorepo 🧐

[codecov]

Codecov Report

Merging #104 into master will increase coverage by 0.1%.
The diff coverage is 100%.

Impacted Files	Coverage Δ
src/index.js	94.54% <100%> (+0.1%)	⬆️

[codecov]

Codecov Report

Merging #104 into master will increase coverage by 0.1%.
The diff coverage is 100%.

Impacted Files	Coverage Δ
src/index.js	94.54% <100%> (+0.1%)	⬆️

[tleunen]

Thanks for digging into the issue and sending a PR.
Could you check if we could use the exposed functions from babel to know where the config is instead of relying on another package?

[tleunen]

Funny how I was thinking to deprecate the library as there should be a better "official" way of fetching the config now (see babel/babel#7472)