go.mod: upgrade to go 1.17

This change was produced using 'go mod tidy -go=1.17'
with a go command built at CL 315210.

This activates lazy loading, and updates the go.mod file to maintain
the lazy-loading invariants (namely, including an explicit requirement
for every package transitively imported by the main module).

Note that this does *not* prevent users with earlier go versions from
successfully building packages from this module.

For golang/go#36460

Change-Id: If672eca0dad61b3f6050a94c758d605b6586cbc3
Reviewed-on: https://go-review.googlesource.com/c/mod/+/316113
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
diff --git a/go.mod b/go.mod
index 417cd80..e655e59 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module golang.org/x/mod
 
-go 1.12
+go 1.17
 
 require (
 	golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550