Update babel-core 6.7.2 -> 6.7.7.
Update babel-core 6.7.2 -> 6.7.7.

Fixes webpack build issue on node versions 6+.
cloverfield-tools/universal-react-boilerplate,cloverfield-tools/universal-react-boilerplate,ericelliott/universal-react-boilerplate,ericelliott/universal-react-boilerplate