Keep Julia 1.6 in ci.yml

Author: amontoison

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        version: ['lts', '1']
+        version: ['1.6', '1']
         os: [ubuntu-latest, macos-latest, windows-latest]
         arch: [x64]
         allow_failure: [false]
@@ -57,3 +57,4 @@ jobs:
         with:
           file: lcov.info
 
+