Fix post-uploads reference (#1523)

capitalization error results in broken link

website/src/docs/aws-s3.md

@@ -21,7 +21,7 @@ uppy.use(AwsS3, {
 })
 ```
 
-There are broadly two ways of uploading to S3 in a browser. A server can generate a presigned URL for a [PUT upload](https://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectPUT.html), or a server can generate form data for a [POST upload](https://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectPOST.html). Companion uses a POST upload. See [POST Uploads](#post-uploads) for some caveats if you would like to use POST uploads without Companion. See [Generating a presigned upload URL server-side](#example-presigned-url) for an example of a PUT upload.
+There are broadly two ways of uploading to S3 in a browser. A server can generate a presigned URL for a [PUT upload](https://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectPUT.html), or a server can generate form data for a [POST upload](https://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectPOST.html). Companion uses a POST upload. See [POST Uploads](#POST-uploads) for some caveats if you would like to use POST uploads without Companion. See [Generating a presigned upload URL server-side](#example-presigned-url) for an example of a PUT upload.
 
 There is also a separate plugin for S3 Multipart uploads. Multipart in this sense refers to Amazon's proprietary chunked, resumable upload mechanism for large files. See the [`@uppy/aws-s3-multipart`](/docs/aws-s3-multipart) documentation.