Upgrade dependencies in CI

Author: SylvainCorlay

.appveyor.yml

@@ -23,7 +23,7 @@ install:
   - conda update -q conda
   - conda info -a
   - conda install gtest cmake -c conda-forge
-  - conda install xtensor==0.8.2 pytest numpy pybind11==2.1.0 -c conda-forge
+  - conda install xtensor==0.8.3 pytest numpy pybind11==2.1.1 -c conda-forge
   - cmake -G "NMake Makefiles" -D CMAKE_INSTALL_PREFIX=%MINICONDA%\\Library -DBUILD_TESTS=ON .
   - nmake test_xtensor_python
   - nmake install

.travis.yml

@@ -81,7 +81,7 @@ install:
     - conda update -q conda
     # Useful for debugging any issues with conda
     - conda info -a
-    - conda install xtensor==0.8.2 pytest numpy pybind11==2.1.0 -c conda-forge
+    - conda install xtensor==0.8.3 pytest numpy pybind11==2.1.1 -c conda-forge
     - cd test
     - conda env create -f ./test-environment.yml
     - source activate test-xtensor-python