fix:make sure event chan consume quickly to prevent deadlock

[ningmingxiao]

I find a dead lock

goroutine 62 [chan send, 10621 minutes]:
github.com/fsouza/go-dockerclient.(*Client).eventHijack.func1(0xc00018c0c0?, 0xc00019a090?)
         github.com/fsouza/go-dockerclient/event.go:353 +0x265
created by github.com/fsouza/go-dockerclient.(*Client).eventHijack
         github.com/fsouza/go-dockerclient/event.go:329 +0x42b

goroutine 19 [sync.RWMutex.Lock, 10621 minutes]:
sync.runtime_SemacquireRWMutex(0xc00018c480?, 0x40?, 0xc00037df20?)
        /usr/local/go/src/runtime/sema.go:87 +0x26
sync.(*RWMutex).Lock(0x5f5e100?)
        /usr/local/go/src/sync/rwmutex.go:152 +0x71
github.com/fsouza/go-dockerclient.(*eventMonitoringState).updateLastSeen(0xc00018c0c0, 0xc0001f5400)
         github.com/fsouza/go-dockerclient/event.go:288 +0x46
github.com/fsouza/go-dockerclient.(*eventMonitoringState).monitorEvents(0xc00018c0c0, 0xc00019a090)
         github.com/fsouza/go-dockerclient/event.go:219 +0x1c5
created by github.com/fsouza/go-dockerclient.(*eventMonitoringState).enableEventMonitoring
         github.com/fsouza/go-dockerclient/event.go:177 +0x159

@fsouza

[ningmingxiao]

can you review this pr ? thank you @fsouza
ping @fsouza

[fsouza]

Thanks for the fix!

[ningmingxiao]

thanks @fsouza