↙️  Minified CSS in AMP default template
↙️  Minified CSS in AMP default template

closes #7314

Minified the CSS in the default `amp.hbs` template.

ErisDS/Ghost,BlueHatbRit/Ghost,cwonrails/Ghost,TryGhost/Ghost,janvt/Ghost,acburdine/Ghost,acburdine/Ghost,ErisDS/Ghost,Kikobeats/Ghost,dbalders/Ghost,acburdine/Ghost,dbalders/Ghost,BlueHatbRit/Ghost,sebgie/Ghost,Kikobeats/Ghost,bitjson/Ghost,JohnONolan/Ghost,kevinansfield/Ghost,bitjson/Ghost,Gargol/Ghost,Kikobeats/Ghost,mohanambati/Ghost,cwonrails/Ghost,JohnONolan/Ghost,cwonrails/Ghost,TryGhost/Ghost,Gargol/Ghost,chevex/undoctrinate,mohanambati/Ghost,sebgie/Ghost,TryGhost/Ghost,e10/Ghost,kevinansfield/Ghost,janvt/Ghost,JohnONolan/Ghost,mohanambati/Ghost,e10/Ghost,dbalders/Ghost,kevinansfield/Ghost,ErisDS/Ghost,sebgie/Ghost