Fix #471: Update readme links (#472)

Author: Arhell

README.md

@@ -19,7 +19,7 @@ Documentation is at [docs/guide/README.md](docs/guide/README.md).
 Installation
 ------------
 
-The preferred way to install this extension is through [composer](http://getcomposer.org/download/):
+The preferred way to install this extension is through [composer](https://getcomposer.org/download/):
 
 ```
 php composer.phar require --prefer-dist yiisoft/yii2-queue