Revert "Disable code cov in CI (#476)" (#483)

This reverts commit fda5e5f.

Author: adrianeboyd

azure-pipelines.yml

@@ -93,5 +93,8 @@ jobs:
       pip install "torch==1.7.1+cpu" -f https://download.pytorch.org/whl/torch_stable.html
       pip install ipykernel pydot graphviz
       python -m ipykernel install --name thinc-notebook-tests --user
-      python -m pytest --pyargs thinc
+      python -m pytest --pyargs thinc --cov=thinc --cov-report=xml
     displayName: 'Run tests'
+
+  - bash: bash <(curl -s https://codecov.io/bash)
+    displayName: 'Upload to codecov.io'