update code mirror component style
update code mirror component style

the ensures the embedded code mirror fills the component space

phosphorjs/phosphor,KesterTong/phoshpor-notebook,Carreau/phosphor-notebook-old-orig,blink1073/phosphor,blink1073/phosphor,Carreau/phosphor-notebook-old-orig,dwillmer/phosphor,dwillmer/phosphor,Carreau/phosphor-notebook-old-orig,dwillmer/phosphor,dwillmer/phosphor,phosphorjs/phosphor,KesterTong/phoshpor-notebook,KesterTong/phoshpor-notebook