docs: Update for version 2.8

Author: ghusta

README.md

@@ -17,7 +17,7 @@ This allows you to run a SMTP server for testing applications which send mail. E
 
 Starting a container :
 
-    docker run -d -p 2525:25 -v /tmp/fakemail:/var/mail ghusta/fakesmtp:2.7
+    docker run -d -p 2525:25 -v /tmp/fakemail:/var/mail ghusta/fakesmtp:2.8
 
 See also docker usage on the [original project](https://github.com/Nilhcem/FakeSMTP#usage-on-docker).