Derive from alpine 3.4 instead of 3.2
Derive from alpine 3.4 instead of 3.2

To work around known vulnerabilities in alpine 3.2 such as CVE-2016-2177
and CVE-2016-2178.

See https://github.com/kylemanna/docker-openvpn/issues/140

elie195/docker-openvpn,kylemanna/docker-openvpn,myplacedk/docker-openvpn,slamont/docker-openvpn,hjnijlunsing/docker-openvpn-armhf