Update appveyor.yml

appveyor.yml

@@ -26,7 +26,7 @@ install:
   - cmd: activate test_env
   - cmd: conda config --add channels conda-forge
   - cmd: conda install -c conda-forge pvl protobuf gdal numpy pandas sqlalchemy pyyaml networkx affine h5py scipy
-  - cmd: conda install pytest-cov
+  - cmd: conda install -c conda-forge pytest pytest-cov
   # https://pythonhosted.org/CodeChat/appveyor.yml.html
   - cmd: python -m pip install -U pip
   - cmd: python -m easy_install -U setuptools