toolchain file not properly overriden

[fprasx]

Related: #26 #28

It seems like the fix from #30 does not properly override the toolchain specified by rust-toolchain.toml. Using rustup override set $TOOLCHAIN instead of rustup default $TOOLCHAIN seems to do the trick:

I can make a PR if this seems like a desirable fix.

[robjtede]

Good catch! Seems reasonable, I'd approve a PR for this suggested fix 👍🏻

[fprasx]

Sounds good: see #33.