Fix rubocop links to point to the right version.

Fixes #2 

@jrafanie or @brandondunne Please review.

Example URL:
old: http://rubydoc.info/gems/rubocop/frames/Rubocop/Cop/Style/AlignHash
new: http://rubydoc.info/gems/rubocop/0.21.0/Rubocop/Cop/Style/AlignHash
Nice, I didn't know you can join like that, (string, Array).  it makes total sense and in this case you don't have to worry about manually constructing the path with the slash.

```ruby
File.join("/abc", ["d", "e"])
=> "/abc/d/e"
```