[smuxi/stable] Travis-CI: use official C# support with multiple Mono versions

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

commit 1cf78eec4eea712100cb98a16b5e2d29016b577a
Author: Mirco Bauer <meebey meebey net>
Date:   Sun Nov 19 17:03:44 2017 +0800

    Travis-CI: use official C# support with multiple Mono versions
    
    Switch to the official [C# support of Travis][0]. When Smuxi started to use
    Travis there was no native support for C# yet thus the C support was (ab)used
    instead. The C build environment wasn't containing the Monon SDK of course so
    that was done manually as part of the build steps.
    
     [0]: https://docs.travis-ci.com/user/languages/csharp/

 .travis.yml |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)
---
diff --git a/.travis.yml b/.travis.yml
index cdc186d..2ae1321 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,8 +1,18 @@
-language: c
+language: csharp
+dist: trusty
 
 before_install:
   - git submodule update --init --recursive
 
+mono:
+    - latest
+    - 4.6.1
+    - 4.2.3
+    - 4.2.1
+    - 4.0.0
+    - 3.12.0
+    - 2.10.8
+
 install:
     - sudo apt-get update > /dev/null
     - sudo apt-get build-dep smuxi > /dev/null