Speed up node install from ~60s to ~5s

[indirect]

If you download the tarball of the master branch, it’s throttled to like 50kb/sec, and downloading the tarball takes 20-60 seconds. If you download the tarball of the latest tagged release, it does not seem to be throttled at all, and reduces the amount of time the "install node" step takes on my machine down to about 5 seconds total.

[rubys]

Because it is an erb file you may need two backslashes in cut -d\" -f4.

Also, this changes expected test results. You can generate new results using rake test:capture and commit those results.

[rubys]

Testing this out on fly.io:

root@328731ef5e5985:/rails# time curl -sL https://github.com/nodenv/node-build/archive/master.tar.gz | wc -c
330185

real	0m0.163s
user	0m0.022s
sys	0m0.011s

vs

root@328731ef5e5985:/rails# time curl -sL "$(curl -s https://api.github.com/repos/nodenv/node-build/releases/latest | grep 'tarball_url' | cut -d\" -f4)" | wc -c
330008

real	0m0.321s
user	0m0.052s
sys	0m0.005s

[indirect]

Whoa, maybe I ran into a temporary GitHub rate limit? If Fly builders aren't getting rate limited by GitHub, this doesn't seem like a good change. Thanks for testing it yourself!