move relative path in react-sdk to webpack config file
move relative path in react-sdk to webpack config file

otherwise react-sdk can't build anymore with riot-web
in a specific location

vector-im/riot-web,vector-im/vector-web,vector-im/riot-web,vector-im/vector-web,vector-im/vector-web,vector-im/riot-web,vector-im/riot-web,vector-im/riot-web,vector-im/vector-web,vector-im/vector-web,vector-im/riot-web