Update readme.md to include mention of 5.7

The package supports 5.7 and mentions that in the header of the readme but below where there's another list of supported versions 5.7 is missing.

Author: mferrara

README.md

@@ -6,7 +6,7 @@
 [![Quality Score](https://img.shields.io/scrutinizer/g/teamtnt/laravel-scout-tntsearch-driver.svg?style=flat-square)](https://scrutinizer-ci.com/g/teamtnt/laravel-scout-tntsearch-driver)
 [![Total Downloads](https://img.shields.io/packagist/dt/teamtnt/laravel-scout-tntsearch-driver.svg?style=flat-square)](https://packagist.org/packages/teamtnt/laravel-scout-tntsearch-driver)
 
-This package makes it easy to add full text search support to your models with Laravel 5.3/5.4/5.5/5.6.
+This package makes it easy to add full text search support to your models with Laravel 5.3/5.4/5.5/5.6/5.7.
 
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