Indicate 1.13 support on README.

README.md

@@ -1,6 +1,6 @@
 ![# Header](https://i.imgur.com/NNwBkWb.png)
 
-[<img src="https://ci.appveyor.com/api/projects/status/e9h6l9fu137jr5ek?retina=true" height="20.74px"></img>](https://ci.appveyor.com/project/dscalzi/zipextractor) [![](https://img.shields.io/github/license/dscalzi/ZipExtractor.svg)](https://github.com/dscalzi/ZipExtractor/blob/master/LICENSE) ![](https://img.shields.io/badge/Spigot-1.8.x--1.12.x-orange.svg) ![](https://img.shields.io/badge/Java-8+-ec2025.svg) [![](https://discordapp.com/api/guilds/211524927831015424/widget.png)](https://discordapp.com/invite/Fcrh6PT)
+[<img src="https://ci.appveyor.com/api/projects/status/e9h6l9fu137jr5ek?retina=true" height="20.74px"></img>](https://ci.appveyor.com/project/dscalzi/zipextractor) [![](https://img.shields.io/github/license/dscalzi/ZipExtractor.svg)](https://github.com/dscalzi/ZipExtractor/blob/master/LICENSE) ![](https://img.shields.io/badge/Spigot-1.8.x--1.13.x-orange.svg) ![](https://img.shields.io/badge/Java-8+-ec2025.svg) [![](https://discordapp.com/api/guilds/211524927831015424/widget.png)](https://discordapp.com/invite/Fcrh6PT)
 
 ZipExtractor is an administrative utility plugin allowing the compression/extraction of archived files through minecraft command. This plugin is extremely useful for dealing with archives over FTP, which does not provide support for neither compression nor extraction. While using this plugin please note that **there is no undo button**. Overridden files **cannot** be recovered.