doc: Fix require.extensions documentation

1. The stability index must come first, or it messes up the markdown
2. require.extensions is an Object, not an Array.

Close #5387

doc/api/globals.markdown

@@ -63,10 +63,10 @@ value from this object, the next `require` will reload the module.
 
 ### require.extensions
 
-* {Array}
-
     Stability: 0 - Deprecated
 
+* {Object}
+
 Instruct `require` on how to handle certain file extensions.
 
 Process files with the extension `.sjs` as `.js`: