Set LC_NUMERIC=en_US.utf8 to fix issue with Discover page

As explained here (http://community.spotify.com/t5/Help-Desktop-Linux-Mac-and/Discover-page-and-radio-page-not-working-on-Linux-on-my-desktop/m-p/503548#M57375) this seems to solve the issue with the Discover tab not working on some systems.