Undefined method `filter' when trying to use with Ruby 2.1.0 on Linux

Kept getting the following error when I tried out this gem:

```
/home/ignisf/.rvm/gems/ruby-2.1.0@yavor/gems/spectator-1.2.6/lib/spectator.rb:31:in `watch_paths!': undefined method `filter' for #<Listen::Listener:0x00000002ac5920> (NoMethodError)
	from /home/ignisf/.rvm/gems/ruby-2.1.0@yavor/gems/spectator-1.2.6/lib/spectator.rb:89:in `initialize'
	from /home/ignisf/.rvm/gems/ruby-2.1.0@yavor/gems/spectator-emacs-0.2.4/lib/spectator/emacs.rb:476:in `initialize'
	from /home/ignisf/.rvm/gems/ruby-2.1.0@yavor/gems/spectator-emacs-0.2.4/bin/spectator-emacs:32:in `new'
	from /home/ignisf/.rvm/gems/ruby-2.1.0@yavor/gems/spectator-emacs-0.2.4/bin/spectator-emacs:32:in `<top (required)>'
	from /home/ignisf/.rvm/gems/ruby-2.1.0@yavor/bin/spectator-emacs:23:in `load'
	from /home/ignisf/.rvm/gems/ruby-2.1.0@yavor/bin/spectator-emacs:23:in `<main>'
	from /home/ignisf/.rvm/gems/ruby-2.1.0@yavor/bin/ruby_executable_hooks:15:in `eval'
	from /home/ignisf/.rvm/gems/ruby-2.1.0@yavor/bin/ruby_executable_hooks:15:in `<main>'
```

Bumping the version of `spectator` fixed it for me. Also took the liberty to fix a few things that were generating warnings.