doc: fix markdown formatting in primordials.md

PR-URL: nodejs/node#42877
Refs: nodejs/node#38635
Reviewed-By: Beth Griggs <bgriggs@redhat.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Zeyu Yang <himself65@outlook.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Danielle Adams <adamzdanielle@gmail.com>

doc/contributing/primordials.md

@@ -400,6 +400,7 @@ process.on('exit', () => console.log(finallyBlockExecuted)); // true
 
 You can use safe alternatives from primordials that differ slightly from the
 original methods:
+
 * It expects an array (or array-like object) instead of an iterable.
 * It wraps each promise in `SafePromise` objects and wraps the result in a new
   `Promise` instance – which may come with a performance penalty.