fix(vite): fix inspector short key failure

[wzc520pyfm]

hi~, I am working on #547 , but I found vite-plugin-vue-inspector's toggleComboKey was set to '', this makes the default shortcut key for opening the inspector invalid. When I removed it, vite-plugin-vue-inspector's toggleComboKey is working!

After this pr, I plan to add this default shortcut key for inspector to the documentation, as well as how to customize the option of vite-plugin-vue-inspector.