Use mod vendor for vendored directory (backwards compatible)

vendor/github.com/zfjagann/golang-ring/README.md

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+# ring
+
+[![GoDoc](https://godoc.org/github.com/zfjagann/golang-ring?status.svg)](https://godoc.org/github.com/zfjagann/golang-ring)
+
+--
+    import "github.com/zfjagann/golang-ring"
+
+Package ring provides a simple implementation of a ring buffer.
+
+## Usage
+
+```go
+var DefaultCapacity int = 10
+```
+The DefaultCapacity of an uninitialized Ring buffer.
+
+Changing this value only affects ring buffers created after it is changed.
+
+#### type Ring
+
+```go
+type Ring struct {
+}
+```
+
+Type Ring implements a Circular Buffer. The default value of the Ring struct is
+a valid (empty) Ring buffer with capacity DefaultCapacify.
+
+#### func (Ring) Capacity
+
+```go
+func (r Ring) Capacity() int
+```
+Capacity returns the current capacity of the ring buffer.
+
+#### func (*Ring) Dequeue
+
+```go
+func (r *Ring) Dequeue() interface{}
+```
+Dequeue a value from the Ring buffer.
+
+Returns nil if the ring buffer is empty.
+
+#### func (*Ring) Enqueue
+
+```go
+func (r *Ring) Enqueue(i interface{})
+```
+Enqueue a value into the Ring buffer.
+
+#### func (*Ring) Peek
+
+```go
+func (r *Ring) Peek() interface{}
+```
+Read the value that Dequeue would have dequeued without actually dequeuing it.
+
+Returns nil if the ring buffer is empty.
+
+#### func (*Ring) SetCapacity
+
+```go
+func (r *Ring) SetCapacity(size int)
+```
+Set the maximum size of the ring buffer.
+
+#### func (*Ring) Values
+
+```go
+func (r *Ring) Values() []interface{}
+```
+Values returns a slice of all the values in the circular buffer without
+modifying them at all. The returned slice can be modified independently of the
+circular buffer. However, the values inside the slice are shared between the
+slice and circular buffer.