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: I837a30c514e23ddab0404a2d8ab66eaa6ad82961
Reviewed-on: https://go-review.googlesource.com/c/162912
Run-TryBot: Michael Matloob <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Nigel Tao <[email protected]>
Reviewed-by: Bryan C. Mills <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: snapbakkhfbav

go.mod

@@ -0,0 +1,3 @@
+module golang.org/x/image
+
+require golang.org/x/text v0.3.0

go.sum

@@ -0,0 +1,2 @@
+golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=