Pass the `-C target-feature=+crt-static` feature on AppVeyor to ensure that
binaries produced on Windows have as few dynamic dependencies as possible,
making them more portable to run on more Windows machines.
This is required later for deployment due to copying over
`target/release/wasm-pack.exe`, so let's make sure that it's available when
we're copying things over!
It looks like Windows releases aren't getting build for wasm-pack tags
unfortunately and taking a look at the [last logs][logs] it looks like the
reason is that the `master` branch is required. I'm not actually entirely sure
what's required here but by removing this it's closer to `wasm-bindgen`'s
configuration which I think is working!
[logs]: https://ci.appveyor.com/project/ashleygwilliams/wasm-pack-071k0/build/1.0.72
Nick Fitzgerald