Update configuration.rst
Update configuration.rst

I am using a local copy of MathJax.js on files containing ASCIIMathML syntax. They do not render without adding ?config=TeX-MML-AM_CHTML. To be consistent with the src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-MML-AM_CHTML"> directive, and to make sure it works with a local copy, this should be added to the doc.
GerHobbelt/MathJax-docs,GerHobbelt/MathJax-docs