Update release-1.18.1.md

Updating to use the right versions in update guidance.

Author: VesaJuvonen

docs/spfx/release-1.18.1.md

@@ -33,7 +33,7 @@ In the project's **package.json** file, identify all SPFx packages. For each SPF
 1. Install the new v1.18.1 package:
 
     ```console
-    npm install @microsoft/{spfx-package-name}@latest --save --save-exact
+    npm install @microsoft/{spfx-package-name}@1.18.1 --save --save-exact
     ```
 
 [!INCLUDE [spfx-release-upgrade-tip](../../includes/snippets/spfx-release-upgrade-tip.md)]