List postgresql as required

Without this, and assuming postgresql has yet to be installed, then `script/bootstrap` fails when building the `pg` gem native extension. The error doesn't make the cause immediately obvious.

I found myself recently bootstrapping a new boxen repo. With a pristine, uncustomized boxen install, and following the *Distribution* section of the `our-boxen` docs leads one here, it seems reasonable to account for not having postgresql installed.
add ruby version to 2.0.0
Install CLTools on 10.10 like we did on 10.9
Allow 10.10 installs
Can't interpolate in single-quotes, duh.

No need to be too specific anyway, let's just be lazy
Automatically install Command Line Tools

Need to credit timsutton/osx-vm-templates
Fix awk regex
Merge pull request #55 from poetic/master

add .ruby-version files
Merge pull request #47 from toolbear/patch-2

List postgresql as a required module
Clean up the output around commandline tools
Auto-merged master into yosemite on deployment
Merge pull request #64 from boxen/yosemite

Yosemite support for CLTools
Fix installs on DP7

Apple radar 18216493 filed 2014-09-03

This manifests as being unable to install gems with C extensions,
because the linker will fail unable to find the CrashReporterSupport
framework
Fix missing underscore
rbconfig.rb is owned by root, so we need sudo

... also quiet down grep
Merge pull request #65 from boxen/dp7-fix

Fix installs on Yosemite DP7
Merge branch 'master' of github.com:boxen/boxen-web