go-ntlm: add go.mod

This file is used by vgo (go get -u golang.org/x/vgo)
and will be understood by Go 1.11 and later too.

Normally a go.mod file lists required dependencies
of a module (think repository), but this module has
no required dependencies, so the file only gives the
module path.

Defining the module path ensures that clients import
the package under its canonical name, not under
alternate casings such as

	import "github.com/thomsonREUTERSeIkOn/go-ntlm"

which would otherwise work (since GitHub answers to that path).

Having a go.mod file also makes it possible to work on
this repository outside GOPATH when using vgo or Go 1.11.
That is, the go.mod file makes it possible to

	git clone https://github.com/ThomsonReutersEikon/go-ntlm
	cd go-ntlm
	vgo build ./...
	vgo test ./...

from anywhere, not just inside GOPATH.

go.mod

@@ -0,0 +1 @@
+module github.com/ThomsonReutersEikon/go-ntlm