Update api.mdx (#1200)

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Author: erik-metz

docs/react-testing-library/api.mdx

@@ -421,7 +421,7 @@ Note that the value is held in `result.current`. Think of `result` as a
 
 ### `rerender`
 
-Renders the the previously rendered render-callback with the new props:
+Renders the previously rendered render-callback with the new props:
 
 ```jsx
 import {renderHook} from '@testing-library/react'