add ci test on v1.6 (#138)

Author: hyrodium

.github/workflows/ci.yml

@@ -15,6 +15,7 @@ jobs:
       matrix:
         version:
           - '1.0'
+          - '1.6'
           - '1' # automatically expands to the latest stable 1.x release of Julia
           - nightly
         os: