Links from Moment docs to Luxon docs broken

[mikebeaton]

A few links from Moment docs to Luxon docs are currently broken (presumably because of Luxon doc layout update at some point), as follows:

• https://moment.github.io/luxon/docs/manual/why.html should be https://moment.github.io/luxon/#/why
• https://moment.github.io/luxon/docs/manual/moment.html should be https://moment.github.io/luxon/#/moment
• https://moment.github.io/luxon/docs/manual/matrix.html should be https://moment.github.io/luxon/#/matrix

Fixed by #725.

[verhovsky]

A lot of people have tried to fix it

https://github.com/moment/momentjs.com/pulls?q=is%3Apr+luxon+