We know that sometimes the guys from ubuntu don't update repositories with latest versions of software, so there is quick way to use official nginx repo for installing it. 
#Add nginx keys
wget -O - http://nginx.org/keys/nginx_signing.key | sudo apt-key add -

#Backup current sources
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak

#Add following repositories to `/etc/apt/sources.list`
echo "deb http://nginx.org/packages/mainline/ubuntu/ trusty nginx" | sudo tee -a /etc/apt/sources.list
echo "deb-src http://nginx.org/packages/mainline/ubuntu/ trusty nginx" | sudo tee -a /etc/apt/sources.list

#Update repositories and install nginx
sudo apt-get update
sudo apt-get install nginx