Update mattermost library (#2152)

* Update mattermost library

* Fix linting

vendor/github.com/hashicorp/yamux/util.go

@@ -0,0 +1,43 @@
+package yamux
+
+import (
+	"sync"
+	"time"
+)
+
+var (
+	timerPool = &sync.Pool{
+		New: func() interface{} {
+			timer := time.NewTimer(time.Hour * 1e6)
+			timer.Stop()
+			return timer
+		},
+	}
+)
+
+// asyncSendErr is used to try an async send of an error
+func asyncSendErr(ch chan error, err error) {
+	if ch == nil {
+		return
+	}
+	select {
+	case ch <- err:
+	default:
+	}
+}
+
+// asyncNotify is used to signal a waiting goroutine
+func asyncNotify(ch chan struct{}) {
+	select {
+	case ch <- struct{}{}:
+	default:
+	}
+}
+
+// min computes the minimum of two values
+func min(a, b uint32) uint32 {
+	if a < b {
+		return a
+	}
+	return b
+}