Change Windows build from 32 to 64 bit

[DanielSWolf]

The rhubarb.exe binary built for Windows is still a 32-bit file. This makes little sense because there are hardly any 32-bit Windows installations any more. What's more, under certain conditions (long audio segments without pauses) Rhubarb may attempt to allocate more than the 2 GB of memory available to 32-bit processes, crashing the application.

The published binary for Windows should be 64 bit, just like the binaries for macOS and Linux.