[markdown demo] Include javascript mode
[markdown demo] Include javascript mode

Closes #6011

hackmdio/CodeMirror,nightwing/CodeMirror,wingify/CodeMirror,codio/CodeMirror,dperetti/CodeMirror,nightwing/CodeMirror,hackmdio/CodeMirror,codio/CodeMirror,wingify/CodeMirror,pabloferz/CodeMirror,pabloferz/CodeMirror,hackmdio/CodeMirror,pabloferz/CodeMirror,dperetti/CodeMirror,nightwing/CodeMirror,codio/CodeMirror,dperetti/CodeMirror,wingify/CodeMirror