Fix Travis CI build (nsubstitute#550)

From [1] [1]: https://travis-ci.community/t/c-builds-are-failing-net-core-installation-error/3063
dtchepak · Apr 23, 2019 · 89565f9 · 89565f9
1 parent ae57666
commit 89565f9
Showing 1 changed file with 1 addition and 0 deletions.
diff --git a/.travis.yml b/.travis.yml
@@ -1,4 +1,5 @@
 language: csharp
+dist: xenial
 dotnet: 2.1.502
 mono: none
 env: CONFIGURATION=Release FRAMEWORK=netcoreapp2.1