Update Jack_and_Loopback_device_as_Alsa-to-Jack_bridge.md

Firefox and Chrome fail to open the pcm.!default device and use the bridge for jplayer audio. This update describes a fix extracted from a bug fix thread (https://bugzilla.mozilla.org/show_bug.cgi?id=812900#c14)
Merge pull request #6 from fafaman/patch-1

Update Jack_and_Loopback_device_as_Alsa-to-Jack_bridge.md