docs: use consistent spelling for TypeScript

... inspired by https://effectivetypescript.com/2021/02/03/pet-peeves/

Author: leschdom

.github/PULL_REQUEST_TEMPLATE.md

@@ -37,7 +37,7 @@ merge of your pull request!
 - [ ] Documentation added to the
       [docs site](https://github.com/testing-library/testing-library-docs)
 - [ ] Tests
-- [ ] Typescript definitions updated
+- [ ] TypeScript definitions updated
 - [ ] Ready to be merged
       <!-- In your opinion, is this ready to be merged as soon as it's reviewed? -->
 

CONTRIBUTING.md

@@ -35,11 +35,11 @@ sure to include those changes (if they exist) in your commit.
 ### Update Typings
 
 If your PR introduced some changes in the API, you are more than welcome to
-modify the Typescript type definition to reflect those changes. Just modify the
-`/types/index.d.ts` file accordingly. If you have never seen Typescript
+modify the TypeScript type definition to reflect those changes. Just modify the
+`/types/index.d.ts` file accordingly. If you have never seen TypeScript
 definitions before, you can read more about it in its
 [documentation pages](https://www.typescriptlang.org/docs/handbook/declaration-files/introduction.html).
-Though this library itself is not written in Typescript we use
+Though this library itself is not written in TypeScript we use
 [dtslint](https://github.com/microsoft/dtslint) to lint our typings.
 
 ## Help needed