fixed typos

Author: mtrezza

README.md

@@ -58,13 +58,13 @@ You can modify the script to use any other API you like or debug-step through th
 An example configuration to add the API Mail Adapter to Parse Server could look like this:
 
 ```js
-const Mailgun = require("mailgun.js");
-const formData = require("form-data");
-const { ApiPayloadConverter } = require("parse-server-api-mail-adapter");
+const Mailgun = require('mailgun.js');
+const formData = require('form-data');
+const { ApiPayloadConverter } = require('parse-server-api-mail-adapter');
 
 // Configure mail client
 const mailgun = new Mailgun(formData);
-const mailgunClient = mailgun.client({ username: "api", key: process.env.MAILGUN_API_KEY });
+const mailgunClient = mailgun.client({ username: 'api', key: process.env.MAILGUN_API_KEY });
 const mailgunDomain = process.env.MAILGUN_DOMAIN;
 
 // Configure Parse Server