Recommend Node 14 instead of 12

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

doc/install/requirements.md

@@ -80,7 +80,7 @@ From GitLab 13.1:
 Beginning in GitLab 12.9, we only support Node.js 10.13.0 or higher, and we have dropped
 support for Node.js 8. (Node.js 6 support was dropped in GitLab 11.8)
 
-We recommend Node 12.x, as it's faster.
+We recommend Node 14.x, as it's faster.
 
 GitLab uses [webpack](https://webpack.js.org/) to compile frontend assets, which requires a minimum
 version of Node.js 10.13.0.