Upload coverage from Azure to codecov.io (#3064)

* WIP: use codecov.io

* Always use bash

* use codecov.token directly

* fixup

* include token directly

Author: shoyer

ci/azure/unit-tests.yml

@@ -13,6 +13,10 @@ steps:
     --cov=xarray --cov-config=ci/.coveragerc --cov-report=xml $EXTRA_FLAGS
   displayName: Run tests
 
+- bash: |
+    bash <(curl https://codecov.io/bash) -t 688f4d53-31bb-49b5-8370-4ce6f792cf3d
+  displayName: Upload coverage to codecov.io
+
   # TODO: publish coverage results to Azure, once we can merge them across
   # multiple jobs: https://stackoverflow.com/questions/56776185