Bump xmlsec version

[aspicer]

xmlsec released a new minor version that doesn't have the insane build issue mentioned on the "develop locally" page for macs anymore
Friendly tip: If you see ERROR: Could not build wheels for xmlsec, refer to this [issue](https://github.com/xmlsec/python-xmlsec/issues/254).

As discussed here: xmlsec/python-xmlsec#284

Bump it.

[aphexcx]

I just noticed this too trying to build posthog locally, why not merge this in?

[aphexcx]

Oh, I just noticed I get this when manually bumping it to 1.3.14:

...site-packages/onelogin/saml2/auth.py", line 14, in <module>
    import xmlsec
xmlsec.InternalError: (-1, 'lxml & xmlsec libxml2 library version mismatch')