Cut down to just two jobs because that is the concurrency limit

Author: oxinabox

.cirrus.yml

@@ -5,9 +5,7 @@ task:
   env:
     matrix:
       - JULIA_VERSION: 1.0
-      - JULIA_VERSION: 1.2
       - JULIA_VERSION: 1.3
-      - JULIA_VERSION: nightly
   install_script:
     - sh -c "$(fetch https://raw.githubusercontent.com/ararslan/CirrusCI.jl/master/bin/install.sh -o -)"
   build_script: