updating socket.io to 0.9.17

fixes #1765. socket.io 0.9.17, among other things, brings in the surespot/channelfix patch which addresses a major redis memory leak. read the full changelog at https://github.com/Automattic/socket.io/blob/0.9.17/History.md
Merge pull request #1939 from chadxz/patch/socket.io-0.9.17

Updating Socket.IO to 0.9.17