design: fix broken link in vgo proposal

Change-Id: I78fffe37d16a33d33f7bb9e81fd5d26386296f08
GitHub-Last-Rev: 8dd0586
GitHub-Pull-Request: #11
Reviewed-on: https://go-review.googlesource.com/102475
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

design/24301-versioned-go.md

@@ -45,7 +45,7 @@ I propose to add versioning to Go using the following approach.
 2. Assign version numbers to modules by tagging specific commits
    with [semantic versions](https://semver.org) such as `v1.2.0`.
    (See
-   the [Defining Go Modules](https://research.swtch.com/vgo-modules) post
+   the [Defining Go Modules](https://research.swtch.com/vgo-module) post
    for details, including how to tag multi-module repositories.)
 
 3. Adopt [semantic import versioning](https://research.swtch.com/vgo-import),