Update ci.yml

Author: ChrisRackauckas

.github/workflows/ci.yml

@@ -5,11 +5,16 @@ on:
 jobs:
   test:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        group:
+          - Core
+        version:
+          - '1'
+          - '1.6'
     steps:
       - uses: actions/checkout@v2
       - uses: julia-actions/setup-julia@v1
-        with:
-          version: 1
       - uses: actions/cache@v1
         env:
           cache-name: cache-artifacts