Update gomod and vendor

vendor/github.com/moby/buildkit/util/throttle/throttle.go

@@ -0,0 +1,58 @@
+package throttle
+
+import (
+	"sync"
+	"time"
+)
+
+// Throttle wraps a function so that internal function does not get called
+// more frequently than the specified duration.
+func Throttle(d time.Duration, f func()) func() {
+	return throttle(d, f, true)
+}
+
+// ThrottleAfter wraps a function so that internal function does not get called
+// more frequently than the specified duration. The delay is added after function
+// has been called.
+func ThrottleAfter(d time.Duration, f func()) func() {
+	return throttle(d, f, false)
+}
+
+func throttle(d time.Duration, f func(), wait bool) func() {
+	var next, running bool
+	var mu sync.Mutex
+	return func() {
+		mu.Lock()
+		defer mu.Unlock()
+
+		next = true
+		if !running {
+			running = true
+			go func() {
+				for {
+					mu.Lock()
+					if next == false {
+						running = false
+						mu.Unlock()
+						return
+					}
+					if !wait {
+						next = false
+					}
+					mu.Unlock()
+
+					if wait {
+						time.Sleep(d)
+						mu.Lock()
+						next = false
+						mu.Unlock()
+						f()
+					} else {
+						f()
+						time.Sleep(d)
+					}
+				}
+			}()
+		}
+	}
+}