try no rasterio in py36 env (#2691)

* try no rasterio in py36 env

* no pynio or iris either

* pin min gdal version in doc build

Author: Joe Hamman

.travis.yml

@@ -60,7 +60,7 @@ script:
   - python --version
   - python -OO -c "import xarray"
   - if [[ "$CONDA_ENV" == "docs" ]]; then
-      conda install -c conda-forge sphinx sphinx_rtd_theme sphinx-gallery numpydoc;
+      conda install -c conda-forge --override-channels sphinx sphinx_rtd_theme sphinx-gallery numpydoc "gdal>2.2.4";
       sphinx-build -n -j auto -b html -d _build/doctrees doc _build/html;
     elif [[ "$CONDA_ENV" == "lint" ]]; then
       pycodestyle xarray ;

ci/requirements-py36.yml

@@ -20,14 +20,14 @@ dependencies:
   - scipy
   - seaborn
   - toolz
-  - rasterio
+  # - rasterio  # xref #2683
   - bottleneck
   - zarr
   - pseudonetcdf>=3.0.1
   - eccodes
   - cdms2
-  - pynio
-  - iris>=1.10
+  # - pynio  # xref #2683
+  # - iris>=1.10    # xref #2683
   - pydap
   - lxml
   - pip: