Set toolchain version

[hybras]

Please commit the toolchain version. This way others can contribute without knowing which nightly version you're using personally.

[mcoblenz]

I had tried to do that, but when I tested it, it didn't seem to have any effect; it still used the system's default version of the toolchain. Can you submit a patch?

[hybras]

sure, what version ru using? also, i couldn't find std::gc in any recent nightly version... was it removed?