Update browser support docs
Update browser support docs

Firefox now ships with MSE and we have polyfills for IE11, neither of
which was reflected in the docs.

Change-Id: I475857718a575a19b0a940e85c17b886b0faf83b

brightcove/shaka-player,tvoli/shaka-player,TobbeEdgeware/shaka-player,TheModMaker/shaka-player,TheModMaker/shaka-player,Ross-cz/shaka-player,cmgrecu/shaka-player,indiereign/shaka-player,sanbornhnewyyz/shaka-player,vimond/shaka-player,baconz/shaka-player,shaka-project/shaka-player,Ross-cz/shaka-player,shaka-project/shaka-player,ustudio/shaka-player,russitto/shaka-player,russitto/shaka-player,baconz/shaka-player,baconz/shaka-player,cmgrecu/shaka-player,vimond/shaka-player,shaka-project/shaka-player,ustudio/shaka-player,tvoli/shaka-player,ustudio/shaka-player,indiereign/shaka-player,ustudio/shaka-player,brightcove/shaka-player,TobbeEdgeware/shaka-player,russitto/shaka-player,sanbornhnewyyz/shaka-player,sanbornhnewyyz/shaka-player,sanbornhnewyyz/shaka-player,indiereign/shaka-player,tvoli/shaka-player,Ross-cz/shaka-player,TobbeEdgeware/shaka-player,TheModMaker/shaka-player,brightcove/shaka-player,TheModMaker/shaka-player,vimond/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,cmgrecu/shaka-player