Say "disconnecting" not "plugging out" your mouse (reactjs#2037)

The previous phrase "plugging out" is uncommon in English. Saying "disconnecting" is better than "unplugging" because many mouse users have wireless mice, and is more accurate.

Author: brendanfalkowski

content/docs/accessibility.md

@@ -421,7 +421,7 @@ There are a number of tools we can use to assist in the creation of accessible w
 
 By far the easiest and also one of the most important checks is to test if your entire website can be reached and used with the keyboard alone. Do this by:
 
-1. Plugging out your mouse.
+1. Disconnecting your mouse.
 1. Using `Tab` and `Shift+Tab` to browse.
 1. Using `Enter` to activate elements.
 1. Where required, using your keyboard arrow keys to interact with some elements, such as menus and dropdowns.