website: hw download links

[zmoon]

I think raw versions of the hw links need to be used if you want people to be able to indeed download the files by right clicking.

e.g.,
https://github.com/mitmath/18S191/raw/master/homework/homework0/hw0.jl
or
https://raw.githubusercontent.com/mitmath/18S191/master/homework/homework0/hw0.jl
for hw0, instead of
https://github.com/mitmath/18S191/blob/master/homework/homework0/hw0.jl

[zmoon]

But I guess if you are just putting the link in Pluto it doesn't matter. Changing to a raw link would enable either manually downloading or copying the link into Pluto though.

[fonsp]

Do you feel like writing this yourself in a PR?