Use mod vendor for vendored directory (backwards compatible)

vendor/github.com/jpillora/backoff/README.md

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+# Backoff
+
+A simple exponential backoff counter in Go (Golang)
+
+[![GoDoc](https://godoc.org/github.com/jpillora/backoff?status.svg)](https://godoc.org/github.com/jpillora/backoff) [![Circle CI](https://circleci.com/gh/jpillora/backoff.svg?style=shield)](https://circleci.com/gh/jpillora/backoff)
+
+### Install
+
+```
+$ go get -v github.com/jpillora/backoff
+```
+
+### Usage
+
+Backoff is a `time.Duration` counter. It starts at `Min`. After every call to `Duration()` it is  multiplied by `Factor`. It is capped at `Max`. It returns to `Min` on every call to `Reset()`. `Jitter` adds randomness ([see below](#example-using-jitter)). Used in conjunction with the `time` package.
+
+---
+
+#### Simple example
+
+``` go
+
+b := &backoff.Backoff{
+	//These are the defaults
+	Min:    100 * time.Millisecond,
+	Max:    10 * time.Second,
+	Factor: 2,
+	Jitter: false,
+}
+
+fmt.Printf("%s\n", b.Duration())
+fmt.Printf("%s\n", b.Duration())
+fmt.Printf("%s\n", b.Duration())
+
+fmt.Printf("Reset!\n")
+b.Reset()
+
+fmt.Printf("%s\n", b.Duration())
+```
+
+```
+100ms
+200ms
+400ms
+Reset!
+100ms
+```
+
+---
+
+#### Example using `net` package
+
+``` go
+b := &backoff.Backoff{
+    Max:    5 * time.Minute,
+}
+
+for {
+	conn, err := net.Dial("tcp", "example.com:5309")
+	if err != nil {
+		d := b.Duration()
+		fmt.Printf("%s, reconnecting in %s", err, d)
+		time.Sleep(d)
+		continue
+	}
+	//connected
+	b.Reset()
+	conn.Write([]byte("hello world!"))
+	// ... Read ... Write ... etc
+	conn.Close()
+	//disconnected
+}
+
+```
+
+---
+
+#### Example using `Jitter`
+
+Enabling `Jitter` adds some randomization to the backoff durations. [See Amazon's writeup of performance gains using jitter](http://www.awsarchitectureblog.com/2015/03/backoff.html). Seeding is not necessary but doing so gives repeatable results.
+
+```go
+import "math/rand"
+
+b := &backoff.Backoff{
+	Jitter: true,
+}
+
+rand.Seed(42)
+
+fmt.Printf("%s\n", b.Duration())
+fmt.Printf("%s\n", b.Duration())
+fmt.Printf("%s\n", b.Duration())
+
+fmt.Printf("Reset!\n")
+b.Reset()
+
+fmt.Printf("%s\n", b.Duration())
+fmt.Printf("%s\n", b.Duration())
+fmt.Printf("%s\n", b.Duration())
+```
+
+```
+100ms
+106.600049ms
+281.228155ms
+Reset!
+100ms
+104.381845ms
+214.957989ms
+```
+
+#### Documentation
+
+https://godoc.org/github.com/jpillora/backoff
+
+#### Credits
+
+Forked from some JavaScript written by [@tj](https://github.com/tj)