Link to Japanese translation

Author: makotot

docs/recipes/when-to-use-plan.md

@@ -1,6 +1,6 @@
 # When to use `t.plan()`
 
-Translations: [Español](https://github.com/sindresorhus/ava-docs/blob/master/es_ES/docs/recipes/when-to-use-plan.md), [Français](https://github.com/sindresorhus/ava-docs/blob/master/fr_FR/docs/recipes/when-to-use-plan.md), [Português](https://github.com/sindresorhus/ava-docs/blob/master/pt_BR/docs/recipes/when-to-use-plan.md)
+Translations: [Español](https://github.com/sindresorhus/ava-docs/blob/master/es_ES/docs/recipes/when-to-use-plan.md), [Français](https://github.com/sindresorhus/ava-docs/blob/master/fr_FR/docs/recipes/when-to-use-plan.md), [日本語](https://github.com/sindresorhus/ava-docs/blob/master/ja_JP/docs/recipes/when-to-use-plan.md),  [Português](https://github.com/sindresorhus/ava-docs/blob/master/pt_BR/docs/recipes/when-to-use-plan.md)
 
 One major difference between AVA and [`tap`](https://github.com/tapjs/node-tap)/[`tape`](https://github.com/substack/tape) is the behavior of `t.plan()`. In AVA, `t.plan()` is only used to assert that the expected number of assertions are called; it does not auto-end the test.