Fix capitalization of Node.js

doc/install/requirements.md

@@ -61,8 +61,8 @@ From GitLab 13.1:
 
 ### Node.js versions
 
-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)
+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.