Migrate build badge to GH Actions (#499)

Merge pull request 499

Author: Rotzbua

docs/README.md

@@ -2,7 +2,7 @@
 
 A Jekyll plugin to add metadata tags for search engines and social networks to better index and display your site's content.
 
-[![Gem Version](https://badge.fury.io/rb/jekyll-seo-tag.svg)](https://badge.fury.io/rb/jekyll-seo-tag) [![Build Status](https://travis-ci.org/jekyll/jekyll-seo-tag.svg)](https://travis-ci.org/jekyll/jekyll-seo-tag)
+[![Gem Version](https://badge.fury.io/rb/jekyll-seo-tag.svg)](https://badge.fury.io/rb/jekyll-seo-tag) [![Build Status](https://github.com/jekyll/jekyll-seo-tag/actions/workflows/ci.yml/badge.svg)](https://github.com/jekyll/jekyll-seo-tag/actions/workflows/ci.yml)
 
 ## What it does