chore(package): update babel-core to version 6.21.0
chore(package): update babel-core to version 6.21.0

https://greenkeeper.io/
brz0/chart-suite,roytang121/oled-visual,liranhershko/intSights,donghee214/pathway,grohaus/schism-ecce-client,grohaus/schism-ecce-client,donghee214/pathway,liranhershko/intSights,roytang121/oled-visual,teemuteemu/sp_modular,hairmot/REACTModuleTest,roytang121/oled-visual,alicoding/react-webpack-babel,brz0/chart-suite,tylerhq/react-fifteen,annaboodle/buddies,teemuteemu/sp_modular,hairmot/REACTModuleTest,alicoding/react-webpack-babel,annaboodle/buddies,kjhwee91/react-c3js,tylerhq/react-fifteen