Use Ubuntu bionic

RehanSaeed · RehanSaeed · commit 160558d6fe83 · 2018-12-24T14:48:57.000Z
diff --git a/.travis.yml b/.travis.yml
@@ -7,7 +7,7 @@ os:
 
 # .NET CLI require Ubuntu 14.04
 sudo: required
-dist: trusty
+dist: bionic
 addons:
   apt:
     packages:
