Update travis to 2.2.203

Author: Jimmy Byrd

.travis.yml

@@ -1,29 +1,22 @@
 language: csharp
 sudo: required
-dist: trusty
+dist: xenial
 
 dotnet: 2.2.203
 mono:
-  - 5.14.0
   - latest # => "stable release"
   - alpha
   - beta
   - weekly # => "latest commits"
 os:
   - linux
 
-addons:
-  apt:
-    packages:
-    - dotnet-sharedframework-microsoft.netcore.app-1.1.2
-
 script:
   - ./build.sh
 
 matrix:
   fast_finish: true
   allow_failures:
-    - mono: latest
     - mono: alpha
     - mono: beta
     - mono: weekly