🐛  Fixed `{{author}}` for post preview
🐛  Fixed `{{author}}` for post preview

- we still need to support the single author usage
- author properties weren't accessible
- added `author` include

TryGhost/Ghost,kevinansfield/Ghost,e10/Ghost,Gargol/Ghost,dbalders/Ghost,dbalders/Ghost,JohnONolan/Ghost,TryGhost/Ghost,ErisDS/Ghost,ErisDS/Ghost,dbalders/Ghost,janvt/Ghost,Kikobeats/Ghost,ErisDS/Ghost,JohnONolan/Ghost,TryGhost/Ghost,chevex/undoctrinate,Kikobeats/Ghost,kevinansfield/Ghost,JohnONolan/Ghost,bitjson/Ghost,bitjson/Ghost,janvt/Ghost,Gargol/Ghost,e10/Ghost,kevinansfield/Ghost,Kikobeats/Ghost