Just install pickle5 for legacy support

Drop the `cloudpickle` hack as we now have a releae with our needs met,
which we included in our requirements. Also ensure we have the latest
`pickle5` with fixes for testing.

continuous_integration/travis/install.sh

@@ -73,8 +73,7 @@ fi
 
 if [[ $PYTHON != 3.8 ]]; then
     # Install backport package for pickle protocol 5 support
-    conda install -c conda-forge -c defaults 'pickle5>=0.0.10'
-    pip install git+https://github.com/jakirkham/cloudpickle.git@opt_use_pickle5_redux
+    conda install -c conda-forge -c defaults 'pickle5>=0.0.11'
     # stacktrace is not currently avaiable for Python 3.8.
     # Remove the version check block below when it is avaiable.
     # For low-level profiler, install libunwind and stacktrace from conda-forge