all: add a go.mod file

This change adds a go.mod and go.sum file to this repo, following the
requirements stated in bcmills's comment here:
https://golang.org/issue/28136#issuecomment-462971974. It's
important to note that we will not be
adding versions to the repo for now.

The change was generated by running "go mod init" and "go mod tidy" using Go
1.11.5 in the top-level directory of the repository.

Updates golang/go#28136

Change-Id: I17b2ac9eaae028a172a5adc260cffba5e0997619
Reviewed-on: https://go-review.googlesource.com/c/162911
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Andrew Bonventre <andybons@golang.org>
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..3a8a43e
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module golang.org/x/crypto
+
+require golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..1936851
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,2 @@
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a h1:1BGLXjeY4akVXGgbC9HugT3Jv3hCI0z56oJR5vAMgBU=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=