vendor: update all dependencies

* Update all dependencies
  * Remove all `[[constraint]]` from Gopkg.toml
  * Add in the minimum number of `[[override]]` to build
  * Remove go get of github.com/inconshreveable/mousetrap as it is vendored
  * Update docs with new policy on constraints

vendor/golang.org/x/time/rate/rate.go

@@ -253,8 +253,12 @@ func (lim *Limiter) waitN(ctx contextContext, n int) (err error) {
 	if !r.ok {
 		return fmt.Errorf("rate: Wait(n=%d) would exceed context deadline", n)
 	}
-	// Wait
-	t := time.NewTimer(r.DelayFrom(now))
+	// Wait if necessary
+	delay := r.DelayFrom(now)
+	if delay == 0 {
+		return nil
+	}
+	t := time.NewTimer(delay)
 	defer t.Stop()
 	select {
 	case <-t.C: