Delete vendored code and update CI to Go 1.13 (#158)

As the Go community transitions to using the modules ecosystem,
we want to only support one way of managing dependencies.
So this change moves to only using Go modules for dependency management.

This means that our effective minimum Go version increases to Go 1.11.
To account for this, we also update:
  - the documentation
  - Makefile
  - CI scripts

1 files changed, 0 insertions, 75 deletions

diff --git a/vendor/golang.org/x/crypto/hkdf/hkdf.go b/vendor/golang.org/x/crypto/hkdf/hkdf.go
deleted file mode 100644
index 5bc2463..0000000
--- a/vendor/golang.org/x/crypto/hkdf/hkdf.go
+++ /dev/null
@@ -1,75 +0,0 @@
-// Copyright 2014 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// Package hkdf implements the HMAC-based Extract-and-Expand Key Derivation
-// Function (HKDF) as defined in RFC 5869.
-//
-// HKDF is a cryptographic key derivation function (KDF) with the goal of
-// expanding limited input keying material into one or more cryptographically
-// strong secret keys.
-//
-// RFC 5869: https://tools.ietf.org/html/rfc5869
-package hkdf // import "golang.org/x/crypto/hkdf"
-
-import (
-	"crypto/hmac"
-	"errors"
-	"hash"
-	"io"
-)
-
-type hkdf struct {
-	expander hash.Hash
-	size     int
-
-	info    []byte
-	counter byte
-
-	prev  []byte
-	cache []byte
-}
-
-func (f *hkdf) Read(p []byte) (int, error) {
-	// Check whether enough data can be generated
-	need := len(p)
-	remains := len(f.cache) + int(255-f.counter+1)*f.size
-	if remains < need {
-		return 0, errors.New("hkdf: entropy limit reached")
-	}
-	// Read from the cache, if enough data is present
-	n := copy(p, f.cache)
-	p = p[n:]
-
-	// Fill the buffer
-	for len(p) > 0 {
-		f.expander.Reset()
-		f.expander.Write(f.prev)
-		f.expander.Write(f.info)
-		f.expander.Write([]byte{f.counter})
-		f.prev = f.expander.Sum(f.prev[:0])
-		f.counter++
-
-		// Copy the new batch into p
-		f.cache = f.prev
-		n = copy(p, f.cache)
-		p = p[n:]
-	}
-	// Save leftovers for next run
-	f.cache = f.cache[n:]
-
-	return need, nil
-}
-
-// New returns a new HKDF using the given hash, the secret keying material to expand
-// and optional salt and info fields.
-func New(hash func() hash.Hash, secret, salt, info []byte) io.Reader {
-	if salt == nil {
-		salt = make([]byte, hash().Size())
-	}
-	extractor := hmac.New(hash, salt)
-	extractor.Write(secret)
-	prk := extractor.Sum(nil)
-
-	return &hkdf{hmac.New(hash, prk), extractor.Size(), info, 1, nil, nil}
-}