Update brunch to 2.10.12 in project generator (#2776)
Update brunch to 2.10.12 in project generator (#2776)

Previous version was 2.10.9. Fixes an issue with source mapping
optikfluffel/phoenix,nshafer/phoenix,mitchellhenke/phoenix,mschae/phoenix,0x00evil/phoenix,Kosmas/phoenix,evax/phoenix,eksperimental/phoenix,mobileoverlord/phoenix,0x00evil/phoenix,michalmuskala/phoenix,Gazler/phoenix,Kosmas/phoenix,mitchellhenke/phoenix,evax/phoenix,jwarwick/phoenix,optikfluffel/phoenix,Joe-noh/phoenix,mobileoverlord/phoenix,rafbgarcia/phoenix,phoenixframework/phoenix,pap/phoenix,rafbgarcia/phoenix,mschae/phoenix,Gazler/phoenix,nshafer/phoenix,eksperimental/phoenix,0x00evil/phoenix,phoenixframework/phoenix,dmarkow/phoenix,pap/phoenix,keathley/phoenix,michalmuskala/phoenix,dmarkow/phoenix,rafbgarcia/phoenix,Joe-noh/phoenix,keathley/phoenix,optikfluffel/phoenix,jwarwick/phoenix,phoenixframework/phoenix,nshafer/phoenix