remove trailing comma

The trailing comma gave me an error when I tried to use `s3sync help sync`

```
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in   
`gem_original_require': /Library/Ruby/Gems/1.8/gems/s3sync-2.0.0/bin/../lib/s3sync/cli.rb:444: syntax error,   
unexpected ')' (SyntaxError)
```