Arcanist installer 1.6.0

Udate php to php 7.0.10 and update arcanist and libphutil to upstream

This is an security update

Switch arcanist and libphutil upstream branch from wmf/stable to wmf/dev,
temporarily.

This is a security update please see

• http://php.net/ChangeLog-7.php#7.0.10
• http://php.net/ChangeLog-7.php#7.0.9