doc,CONTRIBUTING.md: update go version to 1.19

Fixes golang/go#53670

Change-Id: I8aba20ea0fbf82a296c2a8fc464a31a8b3a56beb
GitHub-Last-Rev: 34611e022af28173da869388e578cea7d93d6af7
GitHub-Pull-Request: golang/pkgsite#47
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/416114
Reviewed-by: Jamal Carvalho <jamal@golang.org>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index b46e412..73e494b 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -37,7 +37,7 @@
 
 2. Download the source code for x/pkgsite:
    `git clone https://go.googlesource.com/pkgsite`
-   NOTE: You will need Go 1.18 (as of this writing, the beta2 release) to
+   NOTE: You will need Go 1.19 to
    develop pkgsite.
 
 3. Review the [design document](doc/design.md).
diff --git a/doc/design.md b/doc/design.md
index 9c7fddc..b161396 100644
--- a/doc/design.md
+++ b/doc/design.md
@@ -11,7 +11,7 @@
 
 - A _database_ that stores all information served on the site.
 
-Both services are hosted on App Engine Standard and run Go 1.13. We use a
+Both services are hosted on App Engine Standard and run Go 1.19. We use a
 Postgres database managed by [Google Cloud SQL](https://cloud.google.com/sql).
 
 ![Architecture](architecture.png 'Pkg.go.dev Architecture')