Streamlink: AppVeyor Python33-x64 Broken Builds

[beardypig]

The AppVeyor builds are broken for x64 Python 3.3.
This is due to a new dependency added to pynsist, the new module is scandir. When trying to install scandir the build fails, I'm not down enough with compiling Python module (or anything) on Windows to debug it properly though.

Perhaps someone more in the know can take a look? Otherwise we can work around it by either

1. disabling the Python33-x64 build on AppVeyor; or
2. pinning pynsist to an earlier version (1.11 should still work)

This is affecting all builds since 2017-04-26T09:25:50Z.

Edit: Paging Dr @back-to - your PRs are affected by this :)

[beardypig]

Fixed in #860