Add newline after the match token in error comments (#55)

* Add newline after the match token in error comments

For some reason, Github's rendering of markdown is disabled on any line
that starts with a comment (`<!-- -->`). However, markdown rendering
resumes on the next line.

This is an easy fix which just adds a newline after the match token.

---------

Co-authored-by: Michael Heap <m@michaelheap.com>

index.js

@@ -1,7 +1,7 @@
 const core = require("@actions/core");
 const github = require("@actions/github");
 
-const matchToken = `<!-- reqlabelmessage -->`;
+const matchToken = `<!-- reqlabelmessage -->\n`;
 async function action() {
   try {
     const token = core.getInput("token", { required: true });

index.test.js

@@ -6,7 +6,7 @@ const mockedEnv = require("mocked-env");
 const nock = require("nock");
 nock.disableNetConnect();
 
-const matchToken = `<!-- reqlabelmessage -->`;
+const matchToken = `<!-- reqlabelmessage -->\n`;
 
 describe("Required Labels", () => {
   let restore;