Add libyaml to the requirements (needed for Psych) Updated to use preview2

gistfile1.txt

# First, make sure that you have the most recent rvm. Several bugs with 2.0.0-preview1 & preview 2
# have recently been fixed.
#
# Second, the openssl that comes with MacOS is too old for Ruby 2.0. You need to install
# a newer one with homebrew or the rvm pkg command.

# Option 1, with homebrew openssl:

brew update
brew install libyaml
brew install openssl
rvm get head
rvm install "ruby-2.0.0-preview2" --with-openssl-dir=`brew --prefix openssl`

# Option 2, with rvm pkg install openssl:

rvm get head
rvm pkg install openssl
rvm pkg install libyaml
rvm install "ruby-2.0.0-preview2" --with-openssl-dir=$rvm_path/usr

if compiled failed with output include "Building 'ruby-2.0.0-preview2' using clang - but it's not (fully) supported, expect errors.",
you should append confirgure opts -C --with-gcc=clang , like below 

rvm install "ruby-2.0.0-preview2" --with-openssl-dir=`brew --prefix openssl` -C --with-gcc=clang