Update S3 example URLs to new formats

[mikapfl]

Amazon has streamlined their s3 endpoint naming:

• it is not s3-region in some regions and s3.region in others anymore, it is s3.region everywhere
• if you want IPv6 support (it's about time), you need to use s3.dualstack.region instead.

Updating the example in the chapter on using S3, hopefully most people setting this up will not need to look this info up anymore.

[welcome]

(Image: CC-BY license, The Turing Way Community, & Scriberia. Zenodo. https://doi.org/10.5281/zenodo.3332808) Wohoo! 🎉 Thanks for opening your first pull request to the DataLad Handbook! 😎 We really appreciate your time and effort to contribute to the project - you're amazing! 👏

[adswa]

thank you!

[welcome]

(Image: CC-BY license, The Turing Way Community, & Scriberia. Zenodo. https://doi.org/10.5281/zenodo.3332808) Congrats on merging your first pull request! 🎉 The DataLad Handbook team appreciates your contribution greatly, and we want to say thanks! 💖 Now go ahead and share your first merge with your colleagues, you got yourself this brag right! 😄 🎁

[adswa]

@all-contributors please add @mikapfl for maintenance

[allcontributors]

@adswa

I've put up a pull request to add @mikapfl! 🎉

[adswa]

feel free to add yourself to the .zenodo.json file of this repository (second to last position, in front of Michael Hanke), @mikapfl. Alternatively, feel free to leave your details (Name, affiliation, orcid) in a comment and I'll add you.