[thoughtbot#12] Use clang to install Ruby 1.9.2

ruby

@@ -1,7 +1,7 @@
 #!/bin/sh
 
 echo "Installing Ruby 1.9.2 stable and making it the default Ruby ..."
-  rvm install 1.9.2-p290
+  rvm install 1.9.2-p290 --with-gcc=clang
   rvm use 1.9.2 --default
 
 echo "Installing Rails to write and run web applications ..."