Update .appveyor.yml
Update .appveyor.yml

- Simplify by taking unused column-major layout option out.
- Reactivate fast_finish.
- Work around conda error (https://github.com/conda/conda/issues/6666) by using conda.exe in powershell command
xtensor-stack/xtensor-fftw,egpbos/xtensor-fftw,xtensor-stack/xtensor-fftw,egpbos/xtensor-fftw