az storage blob upload-batch should use '--source' option instead of '-s'

The second example for az storage blob upload-batch uses the shorthand '-s' option key, but this causes an error:

`ERROR: ambiguous option: --s could match --sas-token, --subscription, --source, --socket-timeout`

I think it's better to write '--source' in the full form.

Link to examples: https://docs.microsoft.com/en-us/cli/azure/storage/blob?view=azure-cli-latest#az_storage_blob_upload_batch-examples

---
#### Document Details

⚠ *Do not edit this section. It is required for docs.microsoft.com ➟ GitHub issue linking.*

* ID: 472d5f5f-3ce0-1220-3058-4b27068f512b
* Version Independent ID: 76e1699e-e6ba-c0dd-aad4-c5a7ab58260d
* Content: [az storage blob](https://docs.microsoft.com/en-us/cli/azure/storage/blob?view=azure-cli-latest)
* Content Source: [latest/docs-ref-autogen/storage/blob.yml](https://github.com/MicrosoftDocs/azure-docs-cli/blob/master/latest/docs-ref-autogen/storage/blob.yml)
* Service: **storage**
* GitHub Login: @rloutlaw
* Microsoft Alias: **routlaw**