Fails with Excon 0.19.x

Excon (~> 0.19) has a new initializer in Excon::Connection, which only accepts a hash of params and not a URI string (as before).

### Work-around:

If you walk into issues like:

```
ArgumentError: wrong number of arguments (2 for 1)
        from /usr/local/lib/ruby/gems/1.9.1/gems/excon-0.19.3/lib/excon/connection.rb:44:in `initialize'
  ...
```

Downgrade your Excon gem to 0.18.5