Include core-js and regeneratorruntime polyfills

[chandlerprall]

Closes #70 by including core-js and regeneratorruntime polyfills. I tested this by adding EuiDataGrid to pages/index.tsx, confirmed the error, added the polyfills, confirmed no error.

<EuiDataGrid
  aria-label="hello"
  columns={[
    {
      id: 'test',
    },
  ]}
  columnVisibility={{
    visibleColumns: ['test'],
    setVisibleColumns: () => {},
  }}
  rowCount={10}
  renderCellValue={(stuff) => <span>{stuff.rowIndex}</span>}
/>

I also tried upgrading the EUI version to 67.0.0 but that's causing next to run out of memory during compilation, have to follow up on that one.