Summary:
**Summary**
This should fix install of the metro with npm (issue #142).
We can't have both babylon@6 and babylon@7 as deps for metro package, so as jeanlauliac suggested in https://github.com/facebook/metro/issues/142#issuecomment-368217279 lets create wrapper-package `metro-babylon7` and reexport babylon@7 from it.
**Test plan**
I do manually `yarn && yarn test` - all checks passed.
Closes https://github.com/facebook/metro/pull/143
Differential Revision: D7079144
Pulled By: rafeca
fbshipit-source-id: eeb4f6a01ad92d84dc14702dee07975e253bcf88
Vladimir Timofeev