Bump acorn from 6.2.1 to 6.4.1
Bump acorn from 6.2.1 to 6.4.1

Closes #207

kadoshms/react-jvectormap,kadoshms/react-jvectormap,kadoshms/react-jvectormap,kadoshms/react-jvectormap,kadoshms/react-jvectormap