Removing duplicate "to" word (#520)

Removing duplicate "to" word in "Other Minor Changes 9th points
"

Author: Ahmedfathyarafa

src/guide/migration/introduction.md

@@ -96,7 +96,7 @@ The following consists a list of breaking changes from 2.x:
 - [The `data` option from mixins is now merged shallowly](/guide/migration/data-option.html#mixin-merge-behavior-change)
 - [Attributes coercion strategy changed](/guide/migration/attribute-coercion.html)
 - [Some transition classes got a rename](/guide/migration/transition.html)
-- [When watching an array, the callback will only trigger when the array is replaced. If you need to to trigger on mutation, the `deep` option must be specified.](/guide/migration/watch.html)
+- [When watching an array, the callback will only trigger when the array is replaced. If you need to trigger on mutation, the `deep` option must be specified.](/guide/migration/watch.html)
 - `<template>` tags with no special directives (`v-if/else-if/else`, `v-for`, or `v-slot`) are now treated as plain elements and will result in a native `<template>` element instead of rendering its inner content.
 - In Vue 2.x, application root container's `outerHTML` is replaced with root component template (or eventually compiled to a template, if root component has no template/render option). Vue 3.x now uses application container's `innerHTML` instead - this means the container itself is no longer considered part of the template.