Attempt to fix MacOS CI 3.

.travis.yml

@@ -1,7 +1,7 @@
 language: c # or other C/C++ variants
 
 # xenial is required for GO 1.11.x
-dist: xenial
+# dist: xenial
 sudo: false
 
 # https://docs.travis-ci.com/user/caching/
@@ -16,13 +16,12 @@ cache:
 matrix:
   include:
     - os: linux
-      go:
-        - 1.11.x
+      dist: trusty
+      go: 1.11.x
     - os: osx
+      go: 1.11.x
       before_install:
         - export GOPATH=$HOME/go
-      go:
-        - 1.11.x
 install:
   # build nim from our own branch - this to avoid the day-to-day churn and
   # regressions of the fast-paced Nim development while maintaining the