Bump azure-storage-blob from 2.0.1 to 12.8.1 (#762)

Bumps [azure-storage-blob](https://github.com/Azure/azure-sdk-for-python) from 2.0.1 to 12.8.1.
- [Release notes](https://github.com/Azure/azure-sdk-for-python/releases)
- [Commits](Azure/azure-sdk-for-python@azure-batch_2.0.1...azure-storage-blob_12.8.1)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements_dev_optional.txt

@@ -6,7 +6,7 @@ ipytree==0.2.1
 # optional library requirements for services
 # don't let pyup change pinning for azure-storage-blob, need to pin to older
 # version to get compatibility with azure storage emulator on appveyor (FIXME)
-azure-storage-blob==12.5.0 # pyup: ignore
+azure-storage-blob==12.8.1 # pyup: ignore
 redis==3.5.3
 types-redis
 pymongo==3.11.4