lib: add comment to script eval _tickCallback

Add a comment to match lib/module.js, missed in #11958.

PR-URL: https://github.com/nodejs/node/pull/12050
Ref: https://github.com/nodejs/node/pull/11958
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>

lib/internal/bootstrap_node.js

@@ -401,6 +401,7 @@
                    `${JSON.stringify(name)}, displayErrors: true });\n`;
     const result = module._compile(script, `${name}-wrapper`);
     if (process._print_eval) console.log(result);
+    // Handle any nextTicks added in the first tick of the program.
     process._tickCallback();
   }