Switching does not do what you expect with double digit patch level version numbers

``` shell
$ chruby
  jruby-1.7.24
  jruby-9.0.5.0
  ruby-2.0.0-p648
  ruby-2.1.10
  ruby-2.1.9
  ruby-2.2.4
 * ruby-2.3.0 
$ chruby 2.1
$ chruby
  jruby-1.7.24
  jruby-9.0.5.0
  ruby-2.0.0-p648
  ruby-2.1.10
 * ruby-2.1.9 
  ruby-2.2.4
  ruby-2.3.0
```
