fix: correct JsxEmit value typo from ReactJsx to ReactJSX

Created by: n3tr

• Correct ts.JsxEmit typo from ReactJsx to ReactJSX per https://github.com/microsoft/TypeScript/blob/261d03b8ed317475b34cd782d21710f2020a6312/src/compiler/commandLineParser.ts#L5-L11

Verify steps

• yarn create-react-app my-app --template typescript
• cd my-app
• yarn add typescript@4.1.0-beta
• yarn start