fix(lib): remove unexpected tabindex (#9)

- Fixes the bug that `Table` ended up with `<table>` with an unexpected
  "tabindex" attribute. This bug was caused because Vue 3 no longer
  removes a boolean attribute if its value is "false". `Table` binds
  `undefined` instead of `false` to "tabindex" if `focusable` is `false`
  or not specified.

issue ntohq#8

src/components/table/Table.vue

@@ -52,7 +52,7 @@
             <table
                 class="table"
                 :class="tableClasses"
-                :tabindex="!focusable ? false : 0"
+                :tabindex="!focusable ? undefined : 0"
                 @keydown.self.prevent.up="pressedArrow(-1)"
                 @keydown.self.prevent.down="pressedArrow(1)"
             >