Merge pull request #768 from ReadmeCritic/master

Update README URLs based on HTTP redirects

README.md

 * [Fetch](https://github.com/tedious/Fetch) - An IMAP library.
 * [Mautic](https://github.com/mautic/mautic) - Email marketing automation
 * [PHPMailer](https://github.com/PHPMailer/PHPMailer) - Another mailer solution.
-* [Stampie](https://github.com/henrikbjorn/Stampie) - A library for email services such as [SendGrid](http://sendgrid.com), [PostMark](https://postmarkapp.com), [MailGun](http://www.mailgun.com) and [Mandrill](http://www.mandrill.com).
+* [Stampie](https://github.com/henrikbjorn/Stampie) - A library for email services such as [SendGrid](http://sendgrid.com), [PostMark](https://postmarkapp.com), [MailGun](https://www.mailgun.com/) and [Mandrill](http://www.mandrill.com).
 * [SwiftMailer](http://swiftmailer.org/) - A mailer solution.
 
 ## Files
 *Tools to help install and manage PHP on your computer.*
 
 * [HomeBrew PHP](https://github.com/Homebrew/homebrew-php) - A PHP tap for HomeBrew.
-* [HomeBrew](http://brew.sh/) - A package manager for OSX.
+* [HomeBrew](https://brew.sh/) - A package manager for OSX.
 * [PHP Brew](https://github.com/phpbrew/phpbrew) - A PHP version manager and installer.
 * [PHP Build](https://github.com/php-build/php-build) - Another PHP version installer.
 * [PHP Env](https://github.com/CHH/phpenv) - Another PHP version manager.
 ## PHP Books
 *Fantastic PHP-related books.*
 
-* [Functional Programming in PHP](http://www.functionalphp.com) - This book will show you how to leverage these new PHP5.3+ features by understanding functional programming principles
+* [Functional Programming in PHP](https://www.functionalphp.com/) - This book will show you how to leverage these new PHP5.3+ features by understanding functional programming principles
 * [Grumpy PHPUnit](https://leanpub.com/grumpy-phpunit) - A book about unit testing with PHPUnit by Chris Hartjes.
 * [Mastering Object-Orientated PHP](http://www.brandonsavage.net) - A book about object-orientated PHP by Brandon Savage.
 * [Modern PHP New Features and Good Practices](http://shop.oreilly.com/product/0636920033868.do) - A book about new PHP features and best practices by Josh Lockhart.