Update cors.md documentation

[brunobmello25]

Description

Recent version of golang fiber now breaks if you provide allowOrigins configuration with a space after the comma. For example, if you give the input:

https://first-url.com, https://second-url.com

it breaks with the following error:

2024/02/26 15:01:16.338384 cors.go:124: [Warn] [CORS] Invalid origin format in configuration: https://second-url.com

## Changes Introduced

- Update docs for `docs/api/middleware/cors.md`

- [x] Documentation update (changes to documentation)

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[sixcolors]

This looks like a bug to me.

will confirm shortly.

[sixcolors]

superseeded by #2883