Change nginx version and configuration

Nginx version depends of ubuntu version : 
Maverick = 1.2.7
Lucid, Natty, Oneiric = 1.4.1
Precise, Quantal, Raring, and Saucy > 1.4.1

Script stops during installation (user should press ENTER). This pause will be remove with new version of fabtools : https://github.com/ronnix/fabtools/pull/103