Added correct WebSocket API defaults for protocol.

In the WebSocket API, if the second argument is omitted, it should default to an empty array (not undefined).

> The WebSocket(url, protocols) constructor takes one or two arguments. The first argument, url, specifies the URL to which to connect. The second, protocols, if present, is either a string or an array of strings. If it is a string, it is equivalent to an array consisting of just that string; if it is omitted, it is equivalent to the empty array.

This fix sets the default correctly in ReconnectingWebSocket.