Fix wrong assert and minor typos

src/mailer.js

@@ -92,7 +92,7 @@ function render(templateFile, params, translationAssets) {
 async function sendInvite(user, invitor, email, inviteLink) {
     assert.strictEqual(typeof user, 'object');
     assert.strictEqual(typeof invitor, 'object');
-    assert.strictEqual(typeof invitor, 'string');
+    assert.strictEqual(typeof email, 'string');
     assert.strictEqual(typeof inviteLink, 'string');
 
     const mailConfig = await getMailConfig();