Fix belongsToMany example
Fix belongsToMany example

I noticed that the user model is doing a `belongsToMany(User)` and I
figured you probably meant `belongsToMany(Account)`.

MadcapJake/bookshelf,offlinehacker/bookshelf,shadedprofit/bookshelf,cspotcode/bookshelf,jadengore/bookshelf,joshturn/bookshelf,rbong/bookshelf,sanchesic89/bookshelf,seegno-forks/bookshelf,patbenatar/bookshelf,jordansexton/bookshelf,shaunstanislaus/bookshelf,tjwudi/bookshelf,tjwudi/bookshelf,rbong/bookshelf,VideoAmp/bookshelf,sxhao/bookshelf,lanetix/bookshelf,apla/bookshelf,mdboop/bookshelf,patbenatar/bookshelf,rstacruz/bookshelf,chuym/bookshelf,tbutman/bookshelf,zubeio/bookshelf,TinOo512/bookshelf,joshturn/bookshelf,joshturn/bookshelf,bookshelf/bookshelf,stridentbean/bookshelf,VideoAmp/bookshelf,offlinehacker/bookshelf,MadcapJake/bookshelf,sanchesic89/bookshelf,shaunstanislaus/bookshelf,stonegithubs/bookshelf,zdespolit/bookshelf,stonegithubs/bookshelf,tgriesser/bookshelf,bsiddiqui/bookshelf,mdboop/bookshelf,tgriesser/bookshelf,jadengore/bookshelf,shadedprofit/bookshelf,stridentbean/bookshelf,tbutman/bookshelf,sanchesic89/bookshelf,vellotis/bookshelf,zubeio/bookshelf,zubeio/bookshelf,TNuzzi/bookshelf,vellotis/bookshelf,jadengore/bookshelf,dougshamoo/bookshelf,skevy/bookshelf,jordansexton/bookshelf,rhys-vdw/bookshelf,chuym/bookshelf,zdespolit/bookshelf,VideoAmp/bookshelf,bsiddiqui/bookshelf,seegno-forks/bookshelf,chrisbroome/bookshelf,lanetix/bookshelf,princesust/bookshelf,bookshelf/bookshelf,MadcapJake/bookshelf,tjwudi/bookshelf,chuym/bookshelf,vellotis/bookshelf,princesust/bookshelf,shaunstanislaus/bookshelf,mdboop/bookshelf,zdespolit/bookshelf,TNuzzi/bookshelf,cspotcode/bookshelf,patbenatar/bookshelf,princesust/bookshelf,TinOo512/bookshelf,TNuzzi/bookshelf,dougshamoo/bookshelf,lanetix/bookshelf,skevy/bookshelf,nodeonly/bookshelf,nodeonly/bookshelf,nodeonly/bookshelf,tbutman/bookshelf,offlinehacker/bookshelf,rhys-vdw/bookshelf,skevy/bookshelf,stonegithubs/bookshelf,chrisbroome/bookshelf,stridentbean/bookshelf,sxhao/bookshelf,apla/bookshelf,shadedprofit/bookshelf,sxhao/bookshelf,dougshamoo/bookshelf