add ruby encoding 'magic comment' to file that contains multibyte character

Running under jruby, my application throws a `SyntaxError` due to the presence of a multi-byte character.  
```
SyntaxError: /vendor/bundle/jruby/1.9/gems/filterer-0.1.1/app/helpers/filterer/pagination_helper.rb:22: invalid multibyte char (US-ASCII)
```

This is fixed by adding the "magic comment" to declare the encoding of the file.

cc @adamjacobbecker