Remove explicit test on v1.9 (#153)

This is unnecessary now, given that v1 points to v1.9

Author: jishnub

.github/workflows/ci.yml

@@ -22,7 +22,6 @@ jobs:
         version:
           - '1.6'
           - '1'
-          - '^1.9.0-0'
         os:
           - ubuntu-latest
           - macOS-latest