Update vendor with go dep

This fix updates vendor with `go dep`

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

vendor/github.com/rcrowley/go-metrics/healthcheck.go

@@ -0,0 +1,61 @@
+package metrics
+
+// Healthchecks hold an error value describing an arbitrary up/down status.
+type Healthcheck interface {
+	Check()
+	Error() error
+	Healthy()
+	Unhealthy(error)
+}
+
+// NewHealthcheck constructs a new Healthcheck which will use the given
+// function to update its status.
+func NewHealthcheck(f func(Healthcheck)) Healthcheck {
+	if UseNilMetrics {
+		return NilHealthcheck{}
+	}
+	return &StandardHealthcheck{nil, f}
+}
+
+// NilHealthcheck is a no-op.
+type NilHealthcheck struct{}
+
+// Check is a no-op.
+func (NilHealthcheck) Check() {}
+
+// Error is a no-op.
+func (NilHealthcheck) Error() error { return nil }
+
+// Healthy is a no-op.
+func (NilHealthcheck) Healthy() {}
+
+// Unhealthy is a no-op.
+func (NilHealthcheck) Unhealthy(error) {}
+
+// StandardHealthcheck is the standard implementation of a Healthcheck and
+// stores the status and a function to call to update the status.
+type StandardHealthcheck struct {
+	err error
+	f   func(Healthcheck)
+}
+
+// Check runs the healthcheck function to update the healthcheck's status.
+func (h *StandardHealthcheck) Check() {
+	h.f(h)
+}
+
+// Error returns the healthcheck's status, which will be nil if it is healthy.
+func (h *StandardHealthcheck) Error() error {
+	return h.err
+}
+
+// Healthy marks the healthcheck as healthy.
+func (h *StandardHealthcheck) Healthy() {
+	h.err = nil
+}
+
+// Unhealthy marks the healthcheck as unhealthy.  The error is stored and
+// may be retrieved by the Error method.
+func (h *StandardHealthcheck) Unhealthy(err error) {
+	h.err = err
+}