[smuxi/stable: 12/15] Travis-CI: add Mono versions of current Debian stable Ubuntu LTS

[Mirco M. M. Bauer <mmmbauer src gnome org>]

commit d7597055b3889446384dfcaf736f2631daac3d5a
Author: Mirco Bauer <meebey meebey net>
Date:   Sun Jun 14 23:43:23 2020 +0800

    Travis-CI: add Mono versions of current Debian stable Ubuntu LTS
    
    Debian 10 ships Mono 5.18.0 and Ubuntu 20.04 ships Mono 6.8.0

 .travis.yml | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/.travis.yml b/.travis.yml
index 21c5841b..a2903514 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,6 +6,8 @@ before_install:
 
 mono:
     - latest
+    - 6.8.0
+    - 5.18.0
     - 4.6.2
     - 4.2.3
     - 4.2.1