Added an assertion to ensure connection is established before sending.
Added an assertion to ensure connection is established before sending.

Without this, SocketRocket will raise it's own assertion error, which, while helpful
is not the level at which I'd like to be seeing errors. If I'm trying to call send
before I'm connected, then there is a bug at a higher level in the library.

See #46
alignd/libPusher,hamchapman/libPusher,alignd/libPusher,LoyoChengdu/libPusher,alignd/libPusher,alloy/libPusher,hamchapman/libPusher,lukeredpath/libPusher,lukeredpath/libPusher,alloy/libPusher,LoyoChengdu/libPusher,lukeredpath/libPusher,hamchapman/libPusher,alignd/libPusher,LoyoChengdu/libPusher,alloy/libPusher,LoyoChengdu/libPusher,andreaperizzato/libPusher,andreaperizzato/libPusher,andreaperizzato/libPusher,alloy/libPusher,lukeredpath/libPusher,andreaperizzato/libPusher,hamchapman/libPusher