fix tab whitespace in ci.yml

Author: ablaom

.github/workflows/CI.yml

@@ -18,7 +18,7 @@ jobs:
       matrix:
         version:          
           - '1.0'
-	  - '1.6'
+          - '1.6'
           - '1' # automatically expands to the latest stable 1.x release of Julia
         os:
           - ubuntu-latest