[streann] Added headers for post request
[streann] Added headers for post request

Fixed streamlink/streamlink#1319

gravyboat/streamlink,bastimeyer/streamlink,streamlink/streamlink,back-to/streamlink,javiercantero/streamlink,chhe/streamlink,melmorabity/streamlink,melmorabity/streamlink,streamlink/streamlink,beardypig/streamlink,gravyboat/streamlink,bastimeyer/streamlink,beardypig/streamlink,wlerin/streamlink,back-to/streamlink,javiercantero/streamlink,chhe/streamlink,wlerin/streamlink