Ensure newline after registry string in authutil

Add a newline at the end of the registry string in authutil, to ensure that it's a proper POSIX file.

Author: laat

src/authutil.ts

@@ -43,7 +43,7 @@ function writeRegistryToFile(registryUrl: string, fileLocation: string) {
   const authString: string =
     registryUrl.replace(/(^\w+:|^)/, '') + ':_authToken=${NODE_AUTH_TOKEN}';
   const registryString = `${scope}registry=${registryUrl}`;
-  newContents += `${authString}${os.EOL}${registryString}`;
+  newContents += `${authString}${os.EOL}${registryString}${os.EOL}`;
   fs.writeFileSync(fileLocation, newContents);
   core.exportVariable('NPM_CONFIG_USERCONFIG', fileLocation);
   // Export empty node_auth_token if didn't exist so npm doesn't complain about not being able to find it