_content/ref: add missing `)` in "go.work files" documentation

Change-Id: I8a1f69214f4738bb4bab49200780d997a2948ce8
Reviewed-on: https://go-review.googlesource.com/c/website/+/431615
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
diff --git a/_content/ref/mod.md b/_content/ref/mod.md
index 33b11f0..5abeabe 100644
--- a/_content/ref/mod.md
+++ b/_content/ref/mod.md
@@ -1122,6 +1122,7 @@
 use (
     ./my/first/thing
     ./my/second/thing
+)
 ```
 
 The `go` command provides several subcommands for manipulating `go.work` files.