Mathjax currently has a bug in an upstream library that is incorrectly
loading 'process' because it things it's running under Node.js.

We don't load modules by shortname - so it should be fine to map process to
something else.

Because of the syntax they used we need to map it to something that is already loaded
and evaluates to null (Their code will then assume the module could not be loaded and continue).

We have a handy module that is guaranteed to be loaded first and evaluates to null -> core/first.

We should remove this workaround when MathJax releases a fixed version on their CDN and update the docs.