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, 31 deletions

diff --git a/vendor/golang.org/x/sys/unix/env_unix.go b/vendor/golang.org/x/sys/unix/env_unix.go
deleted file mode 100644
index 84178b0..0000000
--- a/vendor/golang.org/x/sys/unix/env_unix.go
+++ /dev/null
@@ -1,31 +0,0 @@
-// Copyright 2010 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.
-
-// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
-
-// Unix environment variables.
-
-package unix
-
-import "syscall"
-
-func Getenv(key string) (value string, found bool) {
-	return syscall.Getenv(key)
-}
-
-func Setenv(key, value string) error {
-	return syscall.Setenv(key, value)
-}
-
-func Clearenv() {
-	syscall.Clearenv()
-}
-
-func Environ() []string {
-	return syscall.Environ()
-}
-
-func Unsetenv(key string) error {
-	return syscall.Unsetenv(key)
-}