fix(server.go) check server state before send event to channel
This commit fixs a data race between server.Start() and server.send(). Before this commit, server send might receive on a uninitialized stopped channel. To fix this, we initialize the channle before we change the server state to a running state. Then we check the state before receive on the stopped channel.
Merge pull request #215 from xiangli-cmu/fix_channel_race

fix(server.go) check server state before send event to channel