Change Installer to use wp-cli version tested by us

[rahul286]

https://github.com/wp-cli/wp-cli.github.com/blob/master/installer.sh

I think we can pass VERSION to avoid always most recent version getting pulled.

It's better to test wp-cli latest release ourself first, before that making way into EasyEngine.

For now w-cli VERSION will be 0.14

[MiteshShah]

For now w-cli VERSION 0.14.1 is testing to fix the issue #135