allow set CORS_ORIGINS via env vars for heroku
allow set CORS_ORIGINS via env vars for heroku

mrkeng/alerta,skob/alerta,skob/alerta,mrkeng/alerta,mrkeng/alerta,mrkeng/alerta,skob/alerta,guardian/alerta,guardian/alerta,guardian/alerta,guardian/alerta,skob/alerta