use wget instead of curl

[jacobrosenthal]

Closes #23

Hilariously, the rustup script finds curl and attempts to use it again, so it has to be explicitly removed or renamed or something

This fix worksin my project, but when I test it in this repo I get

[main]     Step 11/29 : RUN wget --no-verbose --secure-protocol=TLSv1_2 -qO- https://sh.rustup.rs | sh -s -- -y --default-toolchain `cat rust-toolchain`
[main]      ---> Running in d9329fdd93da
[main]     Aborted (core dumped)

So not sure yet whats different..