Twitter logo update

[SharanRP]

I noticed that the Twitter logo used on your website appears to be outdated. It would be great if the logo could be updated to the current version to maintain consistency and accuracy.

Only this code needs updating. If you think it's relevant, should I proceed with the update?

[nbehrnd]

@SharanRP I assume like for openbabel itself (the application), there might be some automated tests set up. Hence, a PR prepared by you could already be checked by them and then be marked as "passing", or "needs additional intervention" to accelerate the merging update.