eslint-config-react-app typo fix (facebook#10317)

This just fixes a shell snippet in the readme file for this plugin

packages/eslint-config-react-app/README.md

@@ -39,7 +39,7 @@ This config also ships with optional Jest rules for ESLint (based on [`eslint-pl
 You'll first need to add the ESLint plugin for Jest (if you don't already have it installed).
 
 ```sh
-npm install --save-dev eslint-plugin-jest@^24.0.0 eslint-plugin-testing-library&^3.9.0
+npm install --save-dev eslint-plugin-jest@^24.0.0 eslint-plugin-testing-library@^3.9.0
 ```
 
 You can then enable these rules by adding the Jest config to the `extends` array in your ESLint config.