Run CI on pre-release instead of nightly (#151)

Author: sethaxen

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
           - '1.0'
           - '1.6'
           - '1' # automatically expands to the latest stable 1.x release of Julia
-          - nightly
+          - 'pre'
         os:
           - ubuntu-latest
         arch: