Use commander preAction hook for setMode

Hooks are new to commander v8. We can use hooks to ensure that `setMode`
is called before every command is invoked.

package.json

@@ -30,7 +30,7 @@
     "@chrisgavin/safe-which": "^1.0.2",
     "@octokit/plugin-retry": "^3.0.3",
     "@octokit/types": "^5.5.0",
-    "commander": "^6.0.0",
+    "commander": "^8.0.0-1",
     "console-log-level": "^1.4.1",
     "fast-deep-equal": "^3.1.3",
     "file-url": "^3.0.0",