Update SocketIO.java

[ardmn]

public String getHeader had logic error !

public String getHeader(String key) {
        if (this.headers.contains(key)) // headers.contains(param) - get true if map 
                                        //has param value. this method do not  check KEYs in container  !
            return this.headers.getProperty(key);
        return null;
}

I update it like this :

if (headers != null)
   return this.headers.getProperty(key);