Make webpack config node<6 compatible
Make webpack config node<6 compatible

benabraham/cz.pycon.org-2017,benabraham/cz.pycon.org-2017,pyvec/cz.pycon.org-2016,pyvec/cz.pycon.org-2016,pyvec/cz.pycon.org-2016,pyvec/cz.pycon.org-2017,pyvec/cz.pycon.org-2017,pyvec/cz.pycon.org-2017,benabraham/cz.pycon.org-2017