Do not restrict Rake version

This was causing me some grief:

```
Fetching gem metadata from http://rubygems.org/......
Fetching gem metadata from http://rubygems.org/..
Bundler could not find compatible versions for gem "rake":
  In Gemfile:
    ruport (= 1.6.3) ruby depends on
      rake (~> 0.8) ruby

    rails (~> 3.1.7) ruby depends on
      rake (10.0.3)
```