Update README.md to bump up to version v1.6

Author: joshcai

README.md

@@ -48,7 +48,7 @@ GitHub Action for automatically syncing LeetCode submissions to a GitHub reposit
 
        steps:
          - name: Sync
-           uses: joshcai/leetcode-sync@v1.5
+           uses: joshcai/leetcode-sync@v1.6
            with:
              github-token: ${{ github.token }}
              leetcode-csrf-token: ${{ secrets.LEETCODE_CSRF_TOKEN }}