design: fix typo in generics implementation document

Correct the markdown syntax for the second link in the "Generics Implementation - GC Shape Stenciling" document.

This addresses a typo recently introduced in CL 387214.

Change-Id: I96f743b8ebd32ad0ee37118182ddce6161eafbc5
GitHub-Last-Rev: 1a666c4e4385c6c305ef53fed824a88eb240fd53
GitHub-Pull-Request: golang/proposal#43
Reviewed-on: https://go-review.googlesource.com/c/proposal/+/390454
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/design/generics-implementation-gcshape.md b/design/generics-implementation-gcshape.md
index d1b2d17..992524d 100644
--- a/design/generics-implementation-gcshape.md
+++ b/design/generics-implementation-gcshape.md
@@ -3,7 +3,7 @@
 This document describes a method to implement the [Go generics proposal](https://go.googlesource.com/proposal/+/refs/heads/master/design/go2draft-type-parameters.md) by stenciling the code for each different *GC shape* of the instantiated types, and using a *dictionary* to handle differing behaviors of types that have the same shape. 
 
 A more detailed and up-to-date description of the actual implementation released
-in Go 1.18 is given in [this document](https://github.com/golang/proposal/blob/master/design/generics-implementation-dictionaries-go1.18.md
+in Go 1.18 is given in [this document](https://github.com/golang/proposal/blob/master/design/generics-implementation-dictionaries-go1.18.md).
 
 This proposal is middle ground between the [Generics Implementation - Stenciling](https://go.googlesource.com/proposal/+/refs/heads/master/design/generics-implementation-stenciling.md) and [Generics Implementation - Dictionaries](https://go.googlesource.com/proposal/+/refs/heads/master/design/generics-implementation-dictionaries.md) proposals.