Add missing ")" in `gn help config`

Change-Id: Ia3d4e9fe5b99f2f869b198b988255c39d0768799
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/12240
Commit-Queue: Nico Weber <[email protected]>
Commit-Queue: Brett Wilson <[email protected]>
Reviewed-by: Brett Wilson <[email protected]>
diff --git a/docs/reference.md b/docs/reference.md
index 8984ff4..1dde971 100644
--- a/docs/reference.md
+++ b/docs/reference.md
@@ -2172,7 +2172,7 @@
   need to remove the corresponding config that sets it. The final set of flags,
   defines, etc. for a target is generated in this order:
 
-   1. The values specified directly on the target (rather than using a config.
+   1. The values specified directly on the target (rather than using a config).
    2. The configs specified in the target's "configs" list, in order.
    3. Public_configs from a breadth-first traversal of the dependency tree in
       the order that the targets appear in "deps".