Appveyor: Disable fast_finish for now

While builds are randomly failing, fast_finish is counterproductive.

Will reenable this once appveyor stabilizes.

.appveyor.yml

@@ -13,7 +13,6 @@ environment:
   - CONDA: 36
   - CONDA: 27
 matrix:
-  fast_finish: true  # Stop remaining jobs after a job failure
   exclude:
     - image: Visual Studio 2015
       platform: x86