fix: make social container element a span

[dejorrit]

When using SocialIcon inside a <p> element you will see the following warning in your console:

Warning: validateDOMNesting(...): <div> cannot appear as a descendant of <p>.

This is triggered by the social-container div, so setting the as prop has no effect on this warning.

Fixed by changing this div into a span. Since the social-container is positioned absolute this has no visible effects.

[couetilc]

@dejorrit thank you for contributing, released in v6.7.0