Buildr doesn't even build

[Florian Hars]

The build instructions for buildr on ubuntu are missing the dependency
on rake, and even with rake installed, it doesn't build:

$ sudo env JAVA_HOME=$JAVA_HOME gem install buildr
ERROR:  Error installing buildr:
        buildr requires rake (= 0.8.1, runtime)
$ rake --version
rake, version 0.8.1
$

- Florian